Engine Controls - Tests W/codes - Tests (2.2L): Diagnosis Isuzu Amigo II

SELF-DIAGNOSTIC TESTS

Note. Before performing any diagnostic test, refer to TESTS W/CODES - INTRODUCTION article for diagnostic system functions and system diagnostic procedures.

Note. Diagnostic tests were written specifically for use with TECH II scan tool. Other scan tools can be used, but may have limited functions.

Scheme 2

Circuit Description

Engine load is determined using a "speed density" method. This method is calculated using inputs from Manifold Absolute Pressure (MAP) sensor, Crankshaft Position (CKP) sensor, Intake Air Temperature (IAT) sensor and engine RPM. The MAP sensor is the main sensor used to calculate engine load. Powertrain Control Module (PCM) supplies a 5-volt reference signal and a ground circuit to MAP sensor. As manifold pressure changes, MAP sensor input voltage to PCM varies from below 2 volts at idle to above 4 volts at Wide Open Throttle (WOT). If PCM detects MAP sensor input voltage that is out of range or excessively low, DTC P0106 will be set.

Conditions required to set DTC are

1. No ECT, CKP, EGR, EVAP, MAP or TP sensor DTCs present.
2. ECT is above 14°F (-10°C).
3. EGR flow rate is steady, changing less than 2%.
4. Engine speed is steady 1000-4000 RPM, and changing less than 20 RPM.
5. IAC valve counts are steady, changing less than 3 counts.
6. TP sensor position does not vary more than 5%.
7. No status change in brake switch, A/C clutch or power steering pressure switch.
8. MAP value varies more than 10 kPa, for a total of 10 seconds within a 20-second time sample.

Diagnostic Aids

Check for poor connection at PCM: Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Inspect wiring harness for damage. Move connectors and wiring harnesses related to sensor, while observing MAP display on scan tool. A change in display will indicate location of fault. If DTC cannot be duplicated, FAILURE RECORDS data can be used in determining vehicle mileage since DTC was last set. If it is determined that DTC occurs intermittently, performing DTC P1106 or P1107 may isolate cause of fault.

Scheme 3

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. After performing OBD system check, go to next step.
2. With ignition on and engine off, review and record FAILURE RECORDS data on scan tool, then clear the DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Monitor SPECIFIC DTC information. If scan tool indicates that DTC P0106 RAN AND PASSED, go to next step. If scan tool does not indicate DTC P0106 RAN AND PASSED, go to step 4).
3. Check for the following conditions: MAP sensor seal missing or damaged; vacuum hoses disconnected, damaged or incorrectly routed; intake manifold vacuum leaks; throttle body leaks; and EGR valve flange and pipe leaks. Repair as necessary. Retest system. If no problem is found, see Diagnostic Aids.
4. Disconnect MAP sensor connector and observe MAP value displayed on scan tool. Normal reading would show zero volts and 10.3 kPa. If reading is normal, go to step 6). If reading is not normal, go to next step.
5. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a DVOM, check for short to voltage in MAP sensor input circuit between MAP sensor connector and appropriate PCM harness connector terminal. (Scheme 2)and (Scheme 3). If voltage is indicated, locate and repair as necessary. If no voltage is indicated, go to step 12).
6. Turn ignition off. Disconnect PCM harness connectors. Using a DVOM, check continuity of MAP sensor input circuit between MAP sensor connector and appropriate PCM harness connector terminal. Also, check Gray wire for continuity to ground. If continuity does not exist, repair open. If continuity to ground exists, repair short to ground. If continuity exists, and does not exist to ground, go to next step.
7. Connect PCM harness connectors. Turn ignition on. Check MAP sensor connector 5-volt reference terminal for voltage. If reading indicates about 5 volts, go to next step. If reading does not indicate about 5 volts, locate and repair open or shorted condition in 5-volt reference circuit.
8. Turn ignition off. Using a fused jumper wire, connect 5-volt reference circuit to MAP sensor input circuit at MAP sensor connector. Turn ignition on. Observe MAP value displayed on scan tool. If reading is about 5 volts and 104 kPa, go to next step. If reading is not as specified, go to step 12).
9. Turn ignition off. Disconnect PCM harness connectors. Check continuity of MAP sensor ground circuit between MAP sensor connector and appropriate PCM harness connector terminal. If continuity does not exist, repair MAP sensor ground circuit as necessary. If continuity exists, go to next step.
10. Connect PCM harness connectors. Connect DVOM positive lead to MAP sensor connector 5-volt reference terminal, and negative lead to MAP sensor connector ground circuit terminal. Turn ignition on. If reading indicates about 5 volts, go to next step. If reading does not indicate about 5 volts, go to step 12).
11. Replace MAP sensor. Retest system.
12. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

Diagnostic Procedure

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. After performing OBD system check, go to next step.
2. Turn ignition on. With throttle closed, observe MAP value on scan tool. If MAP value indicates zero volts and 10.3 kPa (at sea level), go to step 4). If MAP value does not indicate zero volts and 10.3 kPa, go to next step.
3. With ignition on and engine off, review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions specified. Monitor SPECIFIC DTC information. If scan tool indicates that DTC P0107 failed, go to next step. If scan tool does not indicate DTC P0107 failed, see «DIAGNOSTIC AIDS»(ref-16367-S40813120472001010800000) .
4. Turn ignition off. Disconnect MAP sensor. Using a fused jumper wire, connect 5-volt reference circuit to MAP sensor input circuit at MAP sensor connector. Turn ignition on. Observe MAP value displayed on scan tool. If reading is about 5 volts and 104 kPa, go to step 10). If reading is not as specified, go to next step.
5. Remove jumper wire. Using a test light connected to positive battery voltage, probe MAP sensor input terminal. Observe MAP value displayed on scan tool. If reading is about 5 volts and 104 kPa, go to next step. If reading is not as specified, go to step 8).
6. Turn ignition off. Disconnect PCM harness connectors. Check continuity between appropriate PCM harness connector terminal and MAP sensor 5-volt reference terminal. If continuity does not exist, locate and repair open or short as necessary. Retest system. If continuity exists, go to next step.
7. Inspect PCM harness connector terminals for damage or poor connection. Repair as necessary. If terminals are okay, go to step 11).
8. Turn ignition off. Disconnect PCM harness connectors. Using a DVOM, check MAP sensor input between MAP sensor connector and appropriate PCM harness connector terminal for an open or shorted condition. If an open or shorted condition is indicated, locate and repair as necessary. If MAP sensor input circuit is okay, go to next step.
9. Inspect MAP sensor and PCM harness connectors for damaged terminals or poor terminal connection. Repair as necessary and retest system. If terminals are okay and making good terminal contact, go to next step.
10. Replace MAP sensor and retest system.
11. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. After performing OBD system check, go to next step. NOTE: If the engine idle is rough, unstable or incorrect, repair the idle problem before proceeding.
2. With the engine idling, note the MAP value on scan tool display. If MAP value reading is about 4 volts and 90 kPa, go to step 4). If MAP value reading is not about 4 volts and 90 kPa, go to next step.
3. With ignition on and engine off, review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions specified. Monitor SPECIFIC DTC information. If scan tool indicates that DTC P0108 failed, go to next step. If scan tool does not indicate DTC P0108 failed, see «DIAGNOSTIC AIDS»(ref-16367-S02457619482001010800000).
4. Turn ignition off. Disconnect MAP sensor. Turn ignition on. Observe MAP value displayed on scan tool. If reading is about zero volts and 10.3 kPa, go to next step. If reading is not zero volts and 10.3 kPa, go to step 6).
5. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a DVOM, check MAP sensor input circuit between MAP sensor connector and appropriate PCM harness connector terminal. If voltage is indicated, locate and repair short to voltage in MAP sensor input and retest system. If voltage is not indicated, go to step 12).
6. Turn ignition off. Disconnect PCM harness connectors. Using a DVOM, check continuity of MAP sensor input circuit between MAP sensor connector and appropriate PCM harness connector terminal. (Scheme 2)and (Scheme 3). Also, check MAP sensor input circuit for continuity to ground. If continuity does not exist, repair open in MAP sensor input and retest system. If continuity to ground exists, repair short to ground and retest system. If continuity exists, and does not exist to ground, go to next step.
7. Connect PCM harness connectors. Turn ignition on. Check MAP sensor connector 5-volt reference terminal for voltage. If reading indicates about 5 volts, go to next step. If reading does not indicate about 5 volts, locate and repair open or shorted condition in 5-volt reference circuit. Retest system.
8. Turn ignition off. Using a fused jumper wire, connect 5-volt reference circuit to MAP sensor input circuit at MAP sensor connector. Turn ignition on. Observe MAP value displayed on scan tool. If reading is about 5 volts and 104 kPa, go to next step. If reading is not as specified, go to step 12).
9. Turn ignition off. Disconnect PCM harness connectors. Check continuity of MAP sensor ground circuit between MAP sensor connector and appropriate PCM harness connector terminal. If continuity does not exist, repair MAP sensor ground circuit as necessary. If continuity exists, go to next step.
10. Connect PCM harness connectors. Connect DVOM positive lead to MAP sensor connector 5-volt reference terminal, and negative lead to sensor ground circuit terminal. Turn ignition on. If reading indicates about 5 volts, go to next step. If reading does not indicate about 5 volts, go to step 12).
11. Replace MAP sensor. Retest system.
12. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

Scheme 4

Intake Air Temperature (IAT) sensor is a thermistor, which varies resistance based on temperature. As temperature of sensor increases, resistance decreases. High temperature will result in a low signal voltage. DTC will set when PCM senses IAT sensor voltage is excessively low (shorted to ground).

Conditions required to set DTC are

1. Vehicle driven at 30 MPH or more.
2. Engine running more than 2 minutes.
3. IAT voltage is less than 0.10 volt for 12.5 seconds over a 25-second period.
4. Listed conditions are present for at least 2 seconds.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high voltage wires, such as spark plug cables. If connections and harness appear okay, observe IAT display on scan tool while moving all related harnesses and connectors. A change in scan tool display indicates fault location. Check for skewed IAT sensor. See IAT SENSOR RESISTANCE .

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Using scan tool, read Intake Air Temperature (IAT) value. If temperature is more than 283°F (148°C), go to step 4). If temperature is 283°F (148°C) or less, go to next step.
3. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0112 FAILED THIS IGN, test IAT sensor. Using a DVOM, measure resistance across IAT sensor terminals. See «IAT SENSOR RESISTANCE»(ref-16367-S23237938962001010800000) . Replace IAT sensor if resistance is not as specified. If scan tool does not display DTC P0112 FAILED THIS IGN, go to «DIAGNOSTIC AIDS»(ref-16367-S07018089612001010800000) . IAT SENSOR RESISTANCE Temperature Resistance 212°F (100°C) 177 Ohms 140°F (60°C) 667 Ohms 95°F (35°C) 1802 Ohms 77°F (25°C) 2796 Ohms 41°F (5°C) 7280 Ohms 23°F (-5°C) 21,450 Ohms -5°F (-15°C) 52,700 Ohms
4. Turn ignition off. Disconnect IAT sensor harness connector. Turn ignition on. Using scan tool, read IAT value. If reading is less than -36°F (-38°C), go to step 6). If reading is -36°F (-38°C) or more, go to next step.
5. Turn ignition off. Disconnect PCM connectors. Check IAT sensor input circuit for short to ground. If no short is found, go to step 7). If short is found, repair as necessary. Retest system.
6. Replace IAT sensor. Retest system.
7. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Using scan tool, read IAT value. If temperature reading is below 5 volts, -36°F (-38°C), go to step 4). If temperature reading is not 5 volts, -36°F (-38°C), go to next step.
3. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0113 FAILED THIS IGN, test IAT sensor. Using a DVOM, measure resistance across sensor terminals. See «IAT SENSOR RESISTANCE»(ref-16367-S23237938962001010800000) table under DTC P0112. Replace IAT sensor if resistance is not as specified. If scan tool does not display DTC P0113 FAILED THIS IGN, go to «DIAGNOSTIC AIDS»(ref-16367-S09735152262001010800000) .
4. Turn ignition off. Disconnect IAT sensor harness connector. Using a fused jumper wire, connect terminals of IAT sensor connector. Turn ignition on. Using scan tool, read IAT value. If reading is zero volts and 284°F (140°C), go to step 6). If reading is not zero volts and 284°F (140°C), go to next step.
5. Turn ignition off. Connect jumper between IAT sensor input and chassis ground terminals of IAT harness connector. Turn ignition on and observe IAT sensor value. If reading is zero volts and 284°F (140°C), go to next step. If reading is not zero volts and 284°F (140°C), go to step 8).
6. Check for poor connections at IAT sensor and connector. Repair as necessary. If terminals and connector are okay, go to next step.
7. Turn ignition off. Disconnect PCM connector. Check IAT sensor ground circuit for an open condition. Repair as necessary. Retest system. If IAT ground circuit is okay, go to step 9).
8. Turn ignition off. Disconnect PCM connector. Check IAT sensor input circuit for an open condition. Repair as necessary. Retest system. If IAT sensor input circuit is okay, then go to next step.
9. Check PCM and harness connector for poor connections or damaged terminals. Repair as necessary. Retest system. If terminals are okay, go to step 11).
10. Replace IAT sensor. Retest system.
11. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

Scheme 5

Engine Coolant Temperature (ECT) sensor is a thermistor or a variable resistor, that varies resistance based on temperature. As temperature of ECT sensor increases, resistance decreases. High temperature will result in a low signal voltage. ECT sensor value will be about 1.5-2.0 volts when engine is fully warmed.

Conditions required to set DTC are

1. Engine running greater than two minutes.
2. ECT sensor signal indicates 302°F (150°C) - .14 volt for12 seconds over a 25-second period.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high voltage wires, such as spark plug cables. If connections and harness appear okay, observe ECT display on scan tool while moving all related harnesses and connectors. A change in scan tool display indicates fault location. Check for skewed ECT sensor. See ECT SENSOR RESISTANCE VALUES .

ECT SENSOR RESISTANCE VALUES

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Using scan tool, read ENG COOL TEMP. If temperature is less than 282°F (139°C), go to step 4). If temperature is 282°F (139°C) or greater, go to next step.
3. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0117 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0117 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(ref-16367-S05780628242001010800000) .
4. Disconnect ECT sensor harness connector. Using scan tool, read ENG COOL TEMP. If reading is -38°F (-39°C), go to step 6). If reading is not as specified, go to next step.
5. Turn ignition off. Disconnect PCM connectors. Check ECT sensor input circuit for shorted condition. If no short is found, go to step 7). If short is found, repair as necessary. Retest system.
6. Replace ECT sensor. Retest system.
7. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Using scan tool, read ENG COOL TEMP. If reading is less than -38°F (-37°C), go to step 4). If reading is -38°F (-37°C) or greater, go to next step.
3. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0118 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0118 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(ref-16367-S37767011532001010800000) .
4. Disconnect ECT sensor harness connector. Using a jumper wire, connect ECT sensor connector terminals. Using scan tool, read ENG COOL TEMP. If temperature is 284°F (140°C), go to step 6). If temperature is not as specified, go to next step.
5. Connect jumper wire between chassis ground and ECT sensor harness connector sensor input circuit. Using scan tool, read ENG COOL TEMP. If reading is 284°F (140°C), go to step 7). If reading is not as specified, go to step 8).
6. Check for faulty connection at ECT sensor. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to step 10).
7. Turn ignition off. Disconnect PCM connectors. Check ECT sensor ground circuit for an open. If open is found, repair as necessary. Retest system. If no open is found, go to step 9).
8. Turn ignition off. Disconnect PCM connectors. Check ECT sensor input circuit for an open. If open is found, repair as necessary. Retest system. If no open is found, go to next step.
9. Check for faulty ECT sensor input or ground circuit connection at PCM. If problem is found, repair as necessary. Retest system. If no problem is found, go to step 11).
10. Replace ECT sensor. Retest system.
11. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

Scheme 6

Throttle Position (TP) sensor measures amount of throttle plate opening. PCM uses TP sensor information for fuel delivery calculations. TP sensor reading during Wide Open Throttle (WOT) is about 4.75 volts and 0.25 volts at closed throttle.

Conditions required to set DTC are

1. Engine running and throttle angle is steady at less than 1% change.
2. No MAP, ECT, TP, CKP, EGR, EVAP DTCs set.
3. ECT reading is above 14°F (-10°C).
4. IAC counts are between 10 and 160 counts.
5. MAP value changes by less than 2 kPa.
6. Listed conditions present for 12.5 seconds over a 25-second period.

Check for the following condition(s) and repair as necessary

1. Check TP sensor harness connector terminals for damage.
2. Throttle plate sticking or excessive deposits on throttle plate or throttle bore.
3. Steady throttle movement from a closed to Wide Open Throttle (WOT) should cause TP ANGLE value on scan tool to steadily increase (smoothly) as throttle is opened.

Check for faulty connections or damaged harness. Ensure harness is not routed too close to high voltage wires, such as spark plug cables. If connections and harness appear okay, observe ECT display on scan tool while moving all related harnesses and connectors. A change in scan tool display may indicate a faulty location. Check for skewed MAP signal or faulty MAP sensor by comparing scan tool values of a known-good similar vehicle.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. With ignition on and engine off, review and record FAILURE RECORDS data on scan tool, then clear the DTCs. Operate vehicle within FAILURE RECORDS conditions specified. Monitor SPECIFIC DTC information. If scan tool indicates that DTC P0121 RAN AND PASSED, go to next step. If scan tool does not indicate DTC P0121 RAN AND PASSED, go to step 4).
3. Turn ignition on. While monitoring TP value on scan tool display, move throttle in a smooth even forward motion from closed position to WOT. If value displayed on scan tool changes smoothly from 0% (0.25 volts) to 100% (4.75 volts), go to next step. If TP value change is not smooth or does not change, go to step 11).
4. Turn ignition off. Disconnect TP sensor. Start vehicle and monitor TP value on scan tool. If TP value hold steady within 0-0.25 volts, go to step 6). If TP value does not remain within 0-0.25 volts, go to next step.
5. Turn ignition off. Disconnect all PCM harness connectors. Check for short to voltage in TP sensor input circuit. Repair as necessary. Retest system. If short to voltage is not present, go to step 12).
6. Turn ignition off. Disconnect all PCM harness connectors. Check TP sensor input circuit between TP sensor and PCM connectors for an open or short to voltage condition. Repair as necessary. Retest system. If an open or short is not present, go to next step.
7. Check 5-volt reference circuit between TP sensor and PCM connectors. Turn ignition on. If an open or shorted condition exists, repair as necessary. If an open or shorted condition does not exist, go to next step.
8. Turn ignition off. Using a fused jumper wire, connect TP sensor input circuit and 5-volt reference terminals of TP sensor connector. While monitoring TP value on scan tool, turn ignition on. If TP value indicates about 5 volts and 100%, go to next step. If TP value is not as specified, go to step 12).
9. Turn ignition off. Disconnect all PCM harness connectors. Check TP sensor ground circuit for an open or shorted condition. If such a condition is indicated, repair as necessary. Retest system. If such condition is not present, go to next step.
10. Turn ignition off. Connect all PCM connectors. Using a DVOM, connect positive lead to 5-volt reference circuit terminal, and negative lead to TP sensor ground circuit terminal of TP sensor connector. Turn ignition on. If reading is about 5 volts, go to next step. If reading is not about 5 volts, go to step 12).
11. Replace TP sensor. Retest system.
12. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. With throttle closed, observe scan tool display. If TP sensor value reading is about 0.22 volts, go to step 4). If TP sensor value does not read about 0.22 volts, go to next step.
3. Review and record FAILURE RECORDS data on scan tool. Operate vehicle as recorded from scan tool. Using scan tool, monitor SPECIFIC DTC information for DTC P0122. If scan tool indicates that DTC P0122 failed, go to «DIAGNOSTIC AIDS»(ref-16367-S31901091992001010800000). If scan tool does not indicate DTC P0122 RAN AND PASSED, go to step 5).
4. Turn ignition off. Disconnect TP sensor. Using a fused jumper wire, connect 5-volt reference and TP sensor input terminals of TP sensor harness connector. Turn ignition on. If TP sensor reading is about 5 volts, go to step 9). If reading is not about 5 volts, go to next step.
5. Disconnect jumper wire. Connect a test light between positive battery terminal and TP sensor input circuit terminal of TP sensor connector. If TP sensor value reading on scan tool is about 5 volts, go to next step. If TP sensor value does not read about 5 volts, go to step 8). 6) Turn ignition off. Disconnect PCM. Check 5-volt reference voltage circuit for an open or shorted condition. If a fault is detected, repair as necessary. Retest system. If 5-volt reference circuit is okay, go to next step.
6. Inspect terminals of PCM, TP sensor and harness connectors for poor connection or damaged terminals. Repair as necessary. If terminals and connections are okay, go to step 11).
7. Turn ignition off. Disconnect PCM. Check TP sensor input circuit for an open, shorted to ground or a short to TP sensor ground circuit. If a fault is indicated, repair as necessary. Retest system. If input circuit is okay, go to step 7).
8. Inspect terminals of PCM, TP sensor and harness connectors for poor connection or damaged terminals. (Scheme 3)and (Scheme 6). See «WIRING DIAGRAMS»(ref-16366). Repair as necessary. If terminals and connections are okay, go to next step.
9. Replace TP sensor. Retest system.
10. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on, engine off. Using scan tool, read TP sensor value. If reading is more than 4.78 volts, go to step 4). If reading is 4.78 volts or less, go to next step.
3. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Read SPECIFIC DTC data. If scan tool displays DTC P0123 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0123 FAILED THIS IGN, go to «DIAGNOSTIC AIDS»(ref-16367-S08416139952001010800000) .
4. Turn ignition off. Disconnect TP sensor harness connector. Turn ignition on. Monitor TP SENSOR data. If reading is about zero volts, go to next step. If reading is not as specified, go to step 6).
5. Connect a test light between TP sensor harness connector ground circuit and positive battery terminal. If test light does not illuminate, go to step 10). If test light illuminates, go to step 7).
6. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Check TP sensor signal circuit for a short to voltage. If short to voltage exists, repair as necessary. Retest system. If short to voltage does not exist, go to step 12).
7. Turn ignition on. While monitoring scan tool TP SENSOR display, disconnect each component (one at a time) that shares common 5-volt reference circuit. If display changes, replace component that causes change. Retest system. If display does not change, go to next step.
8. Turn ignition off. Disconnect PCM connectors. Turn ignition on, engine off. Check 5-volt reference circuit between PCM and TP sensor harness connectors for short to voltage. If short is found, repair as necessary. Retest system. If no short is found, go to next step.
9. Check for faulty connection at TP sensor. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to step 11).
10. Turn ignition off. Disconnect PCM connectors. Check for faulty TP sensor ground circuit between PCM and TP sensor harness connectors. Repair as necessary. Retest system. If circuit is okay, go to step 12).
11. Replace TP sensor. Retest system.
12. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. If any related ECT DTCs are set, diagnose affected DTC before proceeding. If no related ECT DTCs are set, go to next step. 3) Allow engine to cool. Check coolant level. If coolant level is low, go to step 9). If coolant level is okay, go to next step.
3. Start engine and allow it to idle. Using scan tool, monitor ENG COOL TEMP. If temperature increases to 70°F (21°C) within 2 minutes, see DIAGNOSTIC AIDS. If specified temperature is not reached within 2 minutes, go to next step.
4. Check thermostat operation. If thermostat is operating correctly, go to next step. If thermostat is not operating correctly, go to step 9).
5. Compare actual coolant temperature with scan tool ECT value. If temperatures are close in value, go to step 9). If temperatures are not close in value, go to next step.
6. Turn ignition off. Disconnect PCM connector(s). Using a DVOM, measure ECT resistance at PCM connector and compare DVOM readings with «ECT SENSOR RESISTANCE VALUES»(ref-16367-S14028866552001010800000) . If chart values equal readings, go to step 12). If chart values do not equal readings, go to next step.
7. Check for an open or shorted condition in wiring between ECT sensor and PCM harness connectors. Also, check for poor connections at ECT sensor and PCM. If a problem is found, go to step 10). If no problem is found, go to step 11).
8. Repair cooling system as necessary. Retest system.
9. Repair wiring and or terminal as necessary. Retest system.
10. Replace ECT sensor. Retest system.
11. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

Scheme 7

PCM provides about .45 volt reference to Heated Oxygen Sensor (HO2S). HO2S sensor signal voltage varies from about one volt when exhaust is rich to about .1 volt when exhaust is lean. PCM reads and stores sensor voltage information during normal closed loop operation and evaluates the voltage samples to determine amount of time sensor voltage is out of range. If HO2S-1 voltage is out of predetermined range, DTC will set.

Conditions required to set DTC are

1. No related DTCs set.
2. ECT is above 140°F (60°C).
3. Closed loop commanded air/fuel ratio is 14.7:1.
4. TP angle is 3-19%.
5. Front HO2S signal reading is below 22 mV during normal closed loop operation for 77 seconds over a 90-second period.

Ensure front HO2S sensor harness is routed correctly and not contacting exhaust system. Check for faulty PCM grounds. Perform FUEL SYSTEM DIAGNOSIS under appropriate TROUBLE SHOOTING in BASIC TESTING article. Perform FUEL INJECTOR BALANCE TEST under FUEL SYSTEM in SYSTEM & COMPONENT TESTS article.

Check for vacuum leaks at intake manifold, throttle body, EGR system and crankcase ventilation system. Check for exhaust leaks before front HO2S. Disconnect MAF sensor connector and see if lean condition is corrected. If lean condition is corrected, check MAF sensor. Check for fuel contamination.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read BANK 1 HO2S-1 value. If reading stays .3 volt or greater, go to next step. If reading stays less than .3 volt, go to step 4).
3. Turn engine off, ignition on. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within FAILURE RECORDS as noted on scan tool. Using scan tool, monitor SPECIFIC DTC information. If scan tool displays DTC P0131 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0131 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(ref-16367-S10074972932001010800000) .
4. Turn ignition off. Disconnect PCM connectors. Check HO2S sensor harness connector signal circuit for shorted condition or for a short to the heater ground circuit. If short is found, go to next step. If no short is found, go to step 6).
5. Repair front HO2S signal circuit as necessary. Retest system.
6. Turn ignition off. Check for continuity between high and low circuits. If continuity exists, go to step 8). If continuity does not exist, go to next step.
7. Repair short between high and low circuits. Retest system.
8. Turn ignition off. Reconnect PCM harness connector, leaving sensor disconnected. Turn ignition on. If scan tool reads 430-450 mV, refer to «DIAGNOSTIC AIDS»(ref-16367-S10074972932001010800000) . If scan tool does not read 430-450 mV, go to next step.
9. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S-1 value. If reading stays greater than 952 mV (500 mV in deceleration fuel cut-off mode), go to step 4). If reading stays 952 mV (500 mV in deceleration fuel cut-off mode) or less, go to next step.
3. Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0132 RAN AND PASSED, go to «DIAGNOSTIC AIDS»(ref-16367-S15469685572001010800000) . If scan tool does not display DTC P0132 RAN AND PASSED, go to next step.
4. Turn ignition off. Disconnect front HO2S harness connector. Turn ignition on. Using a DVOM, measure front HO2S value at high and low signal terminals. If readings are 5-14 volts, go to next step. If readings are not 5-14 volts, go to step 6).
5. Repair short to voltage in signal circuit. Repair as necessary. Retest system.
6. Turn ignition off. Disconnect PCM connectors. Inspect PCM pins and harness connector terminals for damage. Repair as necessary. Retest system.
7. Turn ignition on. Disconnect HO2S and connect a jumper between HO2S high and low circuits to ground. Using a scan tool, read HO2S value. If reading is below 10 mV, go to next step. If reading is 10 mV or above, go to step 9).
8. Replace HO2S. Retest system.
9. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step. NOTE: Diagnose any DTCs set (except for DTCs P1133 or P1134),before proceeding.
2. Start engine and allow it to reach operating temperature. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC TC. If scan tool displays DTC P0133 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0133 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(ref-16367-S19365513922001010800000) .
3. If scan tool also displays DTC P1133 and/or P1134 FAILED THIS IGN, go to step 8). If scan tool does not display these DTCs, go to next step.
4. Visually inspect exhaust system for leaks near front HO2S. If leaks are found, repair as necessary and return to step 2). If no leaks are found, go to next step.
5. Visually inspect front HO2S for secure installation or corrosion on terminals. Check terminal tension at front HO2S and PCM. Check for damaged wiring. If a problem is found, go to step 9). If no problem is found, go to next step.
6. Disconnect front HO2S connector. Turn ignition on. Using a DVOM, measure voltage between high signal circuit and ground, and between low signal circuit and ground. If reading is 3-4 volts, go to next step. If reading is not as specified, go to step 10).
7. Connect a jumper wire between front HO2S harness connector high signal and low signal terminals and ground. Turn ignition on. Using scan tool, read HO2S-1 voltage. If reading is less than 10 mV and immediately returns to 450 mV when jumper wire is removed, go to step 12). If voltage is not as specified, go to step 13).
8. Replace affected HO2S. Retest system. NOTE: Before replacing HO2S, correct cause of HO2S contamination.
9. Repair condition as necessary. Retest system.
10. Inspect PCM connections and terminals for damage. Repair as necessary. Retest system. If PCM connections and terminals are in good condition, go to next step.
11. Repair open, short or grounded front HO2S signal circuit. Retest system.
12. Replace front HO2S. Retest system.
13. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Start engine and allow it to reach normal operating temperature. Apply parking brake and increase engine speed to greater than 1200 RPM for 3 minutes. Using scan tool, read front HO2S-1 voltage. If reading is .4-.5 volt, go to step 4). If reading is not .4-.5 volt, go to next step.
3. Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0134 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0134 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(ref-16367-S31782654702001010800000) .
4. Inspect sensor harness for damage, repair as necessary. Retest system. If harness is okay, go to next step.
5. Check for faulty connection at front HO2S for high and low circuit. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
6. Check for faulty connection at PCM for high and low circuit. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
7. Turn ignition off. Disconnect PCM connectors. Check resistance of front HO2S harness connector signal high circuit. If resistance is greater than .5 ohm, repair open or faulty connection as necessary. Retest system. If resistance is .5 ohm or less, go to next step.
8. Ensure ignition is off and PCM connectors are disconnected. Check resistance of front HO2S harness connector low circuit. If resistance is greater than 5 ohms, repair open or faulty connection as necessary. Retest system. If resistance is 5 ohms or less, go to next step.
9. Turn ignition on, engine off. Disconnect HO2S harness connector. Connect jumper wires from front HO2S harness connector high and low circuits to chassis ground. Using a scan tool, read voltage. If reading is about .10 volt, go to next step. If reading is not about .10 volt, go to step 11).
10. Replace front HO2S. Retest system.
11. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step. NOTE: If engine has been operating, allow engine to cool for about 30 minutes before proceeding with diagnostic testing.
2. Turn ignition on, engine off. Using scan tool, read HO2S-1 value. If reading is greater than .65 volt or less than .25 volt, see «DIAGNOSTIC AIDS»(ref-16367-S07436848782001010800000) . If reading is not as specified, go to next step.
3. Inspect O(2) SENSOR (20-amp) fuse. If fuse is open, go to step 15). If fuse is okay, go to next step.
4. Turn ignition off. Raise and support vehicle. Disconnect front HO2S harness connector. Connect a test light between chassis ground and front HO2S ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
5. Connect test light between front HO2S harness connector ignition feed and heater ground circuits. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
6. Allow front HO2S to cool for at least 10 minutes. Using DVOM, check resistance between ignition feed and heater ground circuits at front HO2S. If resistance is 3-6 ohms, go to step 9). If resistance is not as specified, go to step 10).
7. Repair open front HO2S ignition feed circuit. Retest system.
8. Repair open front HO2S heater ground circuit. Retest system.
9. Check for faulty connection at front HO2S harness connector. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
10. Check for faulty connection at front HO2S ground and signal circuit harness connector. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
11. Turn ignition off. Disconnect PCM connectors. Check resistance of front HO2S signal and ground circuits. If resistance on either circuit is greater than 5 ohms, repair open or faulty connection as necessary. Retest system. If resistance is 5 ohms or less, go to next step.
12. Check for faulty ground circuit connection at PCM. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
13. Check for faulty front HO2S signal circuit connection at PCM. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
14. Replace front HO2S. Retest system.
15. Locate and repair shorted condition in front HO2S ignition feed circuit. Replace fuse. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read BANK 1 HO2S-2 value. If reading remains less than .026 volt, go to step 4). If reading remains .026 volt or greater, go to next step.
3. Turn engine off. Turn ignition on. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0137 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0137 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(ref-16367-S37964636652001010800000) .
4. Turn ignition off. Disconnect PCM connectors. Check rear HO2S sensor harness connector signal circuit and ground circuit for shorted condition. If short is found, go to next step. If no short is found, go to step 6).
5. Repair rear HO2S circuit as necessary. Retest system.
6. With ignition off, leaving PCM and rear HO2S harness connectors disconnected, check continuity in signal and ground circuit. If continuity exists, go to next step. If continuity does not exist, go to step 8).
7. Repair shorts in signal and ground circuits. Retest system.
8. With ignition off, reconnect PCM, leaving HO2S disconnected. Turn ignition on. Using scan tool, read HO2S-2 value. If reading is .43-.45 volts, go to Diagnostic Aids. If reading is not as specified, go to next step.
9. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S-2 value. If reading remains greater than .952 volt, go to step 4). If reading remains .952 volt or less, go to next step.
3. Turn ignition on. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0138. If scan tool displays DTC P0138 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0138 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(ref-16367-S32999909692001010800000) .
4. Turn ignition off. Disconnect rear HO2S connector. Turn ignition on. Using a DVOM, measure voltages at high and low signal terminals of HO2S-2 harness connector. If reading is 5-14 volts, go to next step. If reading is not 5-14 volts, go to step 6).
5. Repair short to voltage in rear HO2S signal circuit. Retest system.
6. Turn ignition off. Disconnect PCM connectors. Inspect PCM pins and terminals for damage. Repair as necessary. Retest system. If no problem is found, go to next step.
7. Turn ignition on. Use jumper wires to connect HO2S-2 sensor high and low signal terminals to chassis ground. Using scan tool, read HO2S-2 value. If reading is under .01 volt, go to next step. If reading is greater than .01 volt, go to step 9).
8. Replace rear HO2S. Retest system.
9. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Start engine and allow it to reach operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, read HO2S-2 value. If reading is switching outside of .425-.475 volt range, go to next step. If reading is within .425-.475, go to step 4).
3. Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0140 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0140 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(ref-16367-S18165974332001010800000) .
4. Check for faulty connection at rear HO2S. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
5. With ignition off, check for faulty connection at PCM. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
6. Turn ignition off. Disconnect PCM connectors. Check resistance of rear HO2S harness connector signal circuit. If resistance is greater than 5 ohms, repair open or faulty connection as necessary. Retest system. If resistance is 5 ohms or less, go to next step.
7. Reconnect PCM harness. Turn ignition on. Using DVOM, check voltage between each rear HO2S harness connector terminal and heater ground circuits. If reading is about 3-4 volts, go to step 9). If reading is not as specified, go to next step.
8. Check both signal circuits for a shorted condition. Repair as necessary. Retest system. If no short exists, go to step 11).
9. Disconnect rear HO2S harness connector. Connect jumper wires between rear HO2S harness connector high and low signal circuits to heater ground terminal. If reading is 0-.01 volt, go to next step. If reading not 0-.01 volt, go to step 11).
10. Replace rear HO2S. Retest system.
11. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step. NOTE: If engine has been operating, allow engine to cool for about 30 minutes before proceeding with diagnostic tests.
2. Turn ignition on, engine off. Using scan tool, read HO2S-2 value. If reading is greater than .65 volt or less than .25 volt, see «DIAGNOSTIC AIDS»(ref-16367-S42512434652001010800000) . If reading is not as specified, go to next step.
3. Inspect O 2 SENSOR (20-amp) fuse. If fuse is open, go to step 15). If fuse is okay, go to next step.
4. Turn ignition off. Raise and support vehicle. Disconnect rear HO2S harness connector. Connect a test light between chassis ground and probe rear HO2S ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
5. Connect test light between rear HO2S harness connector ignition feed and heater ground circuits. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
6. Allow rear HO2S to cool for at least 10 minutes. Using DVOM, check resistance between ignition feed and heater ground circuits at rear HO2S. If resistance is 3-6 ohms, go to step 9). If resistance is not as specified, go to step 10).
7. Repair open rear HO2S ignition feed circuit. Retest system.
8. Repair open rear HO2S heater ground circuit. Retest system.
9. Check for faulty connection at rear HO2S. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
10. Turn ignition off. Disconnect PCM connectors. Check resistance of rear HO2S signal and ground circuits. If resistance on either circuit is greater than 5 ohms, repair open or faulty connection. Retest system. If resistance is 5 ohms or less, go to next step.
11. Check for faulty connection at rear HO2S harness connector. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
12. Check for faulty ground circuit connection at PCM. If faulty connection is found, repair as necessary. If connection is okay, go to next step.
13. Check for faulty rear HO2S signal circuit connection at PCM. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
14. Replace rear HO2S. Retest system.
15. Locate and repair shorted condition in rear HO2S ignition feed circuit and replace fuse. Retest system.

PCM reads HO2S signal voltage and adjusts fuel delivery based on this voltage. A change made to fuel delivery is indicated by Long Term (LT) and Short Term (ST) FUEL TRIM values.

ST FUEL TRIM values change rapidly in response to HO2S signal voltages. These changes fine tune engine fueling. LT FUEL TRIM values change in response to trends in ST fuel trim. LT fuel trim makes coarse adjustments to fueling in order to re-center and restore control to ST fuel trim.

Ideal FUEL TRIM value is about zero. Fuel trim value more than zero indicates PCM is adding fuel to compensate for a lean condition. Fuel trim less than zero indicates PCM is reducing amount of fuel to compensate for rich condition. DTC will set if PCM detects an excessively rich or lean condition.

Conditions required to set DTC are

1. No scan tool test is being run.
2. No emission related DTCs set.
3. ECT is 149-219°F (65-104°C).
4. IAT is -40-248°F (-40-120°C).
5. BARO is more than 72 kPa.
6. Engine speed is 400-6000 RPM.
7. System voltage is greater than 9.5 volts.
8. Engine is operating in closed loop.
9. Average short term fuel trim is greater than .97.
10. Adaptive index multiplier samples is greater than 1.21.

Ensure HO2S wiring is routed correctly and not contacting exhaust system. Check for faulty PCM-to-engine ground connections. Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool HO2S-1 display while moving all related harnesses and connectors. A change in scan tool display indicates fault location. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. If any DTC other than P0171 is set, diagnose affected DTC before proceeding. If no other DTC is set, go to next step.
3. Operate vehicle in closed loop. Using scan tool, read BANK 1 LT FUEL TRIM values. If LT FUEL TRIM value is about 20%, go to step 5). If value is not as specified, go to next step.
4. Using scan tool, read and record FAILURE RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0171 test runs. If scan tool displays DTC P0171 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0171 FAILED THIS IGN, go to «DIAGNOSTIC AIDS»(ref-16367-S29301018282001010800000) .
5. Check vacuum hoses for splits, kinks and proper routing. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
6. Check PCV valve for proper installation. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
7. Start engine. If high or unsteady idle condition exists, go to next step. If idle is okay, go to step 10).
8. Using scan tool, read IDLE AIR CONTROL value. If value is more than 5 counts, go to step 10). If value is 5 counts or less, go to next step.
9. Check throttle body, intake manifold, and EGR valve for vacuum leaks. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
10. Check IAC valve for proper operation. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
11. Check for fuel contamination. If fuel is contaminated, repair condition causing contamination. Retest system. If fuel is okay, go to next step.
12. Check PCM injector, power and sensor grounds for clean and tight connection, and for proper location. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
13. Perform fuel system pressure test. See FUEL PUMP PRESSURE TEST under FUEL SYSTEM in «BASIC TESTING»(ref-16362) article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
14. Ensure evaporative system is functional. See «DTC P0443: EVAP SYSTEM PURGE CONTROL VALVE CIRCUIT MALFUNCTION»(ref-16367-S23658304422001010800000) . If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
15. Check intake manifold, injector "O" rings, EGR adapter, EGR valve, and EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
16. Check exhaust system for leaks, loose or missing hardware. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
17. Perform FUEL INJECTOR BALANCE TEST under FUEL SYSTEM in «SYSTEM & COMPONENT TESTS»(ref-16371) article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
18. Ensure HO2S is installed securely, and connector and harness are not contacting exhaust manifold or ignition wires. If a problem is found, repair as necessary. Retest system. If no problem is found, go to «DIAGNOSTIC AIDS»(ref-16367-S29301018282001010800000) .

PCM reads HO2S signal voltage and adjusts fuel delivery based on this voltage. A change made to fuel delivery is indicated by Long Term (LT) and Short Term (ST) FUEL TRIM values.

ST FUEL TRIM values change rapidly in response to HO2S signal voltages. These changes fine tune engine fueling. LT FUEL TRIM values change in response to trends in ST fuel trim. LT fuel trim makes coarse adjustments to fueling in order to re-center and restore control to ST fuel trim. LT and ST fuel trim can be read by using a scan tool.

Ideal FUEL TRIM value is about zero. Fuel trim value more than zero indicates that PCM is adding fuel to compensate for a lean condition. Fuel trim less than zero indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC will set if PCM detects an excessively rich or lean condition.

Conditions required to set DTC are

1. No scan tool test is being run.
2. No emission related DTCs set.
3. ECT is 149-219°F (65-104°C).
4. IAT is -40-248°F (-40-120°C).
5. BARO is more than 72 kPa.
6. Engine speed is 400-6000 RPM.
7. System voltage is greater than 9.5 volts.
8. Engine is operating in closed loop.
9. Average short term fuel trim is greater than .97.
10. Adaptive index multiplier samples is greater than 1.21.

Check fuel pressure. Check fuel injector operation. Disconnect MAF sensor connector and see if rich condition is corrected. If rich condition is corrected, replace MAF sensor.

Check for faulty TP sensor operation. Check for faulty connections or damaged harness. If connections and harness appear okay, observe HO2S-1 display on scan tool while moving all related harnesses and connectors. A change in scan tool display indicates fault location. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. If any other DTCs are set, other than P0172, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
3. Operate vehicle in closed loop mode while using scan tool to read BANK 1 LT FUEL TRIM values. If BANK 1 LT FUEL TRIM value is less than -14%, go to step 5). If value is not as specified, go to next step.
4. Using scan tool, read and record FAILURE RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0172 test runs. If scan tool displays DTC P0172 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0172 FAILED THIS IGN, go to «DIAGNOSTIC AIDS»(ref-16367-S06703139902001010800000) .
5. Check air filter element condition. Replace air filter element if necessary. Retest system. If air filter element is okay, go to next step.
6. Check air intake duct for being collapsed or restricted. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
7. Start engine. If high or unsteady idle condition exists, go to next step. If idle is okay, go to step 10).
8. Using scan tool, read IDLE AIR CONTROL value. If value is less than 100 counts, go to step 10). If value is 100 counts or more, go to next step.
9. Turn ignition off. Check throttle body bore, throttle plate and IAC passages for coking and foreign objects. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
10. Check IAC valve for proper operation. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
11. Disconnect vacuum hose from fuel pressure regulator and check it for presence of fuel. If fuel is present, replace fuel pressure regulator. Retest system. If no fuel is present, go to next step.
12. Turn ignition on, engine off. Using scan tool, read TP ANGLE while slowly depressing accelerator pedal. If TP ANGLE increases steadily from 0% at closed throttle to 100% at wide open throttle, go to next step. If TP ANGLE does not increase as specified, to step 17).
13. Perform fuel system pressure test. See FUEL PUMP PRESSURE TEST under FUEL SYSTEM in «BASIC TESTING»(ref-16362) article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
14. Ensure evaporative system is functional. See «DTC P0443: EVAP SYSTEM PURGE CONTROL VALVE CIRCUIT MALFUNCTION»(ref-16367-S23658304422001010800000) . If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
15. Perform FUEL INJECTOR BALANCE TEST under FUEL SYSTEM in appropriate «BASIC TESTING»(ref-16362) article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
16. Remove HO2S-1 and check it for silicone (powdery White deposit) contamination. If HO2S-1 is contaminated, replace HO2S-1. Retest system. If HO2S-1 is not contaminated, go to «DIAGNOSTIC AIDS»(ref-16367-S06703139902001010800000) .
17. Check and tighten TP sensor mounting screws. If mounting screws are tight, replace TP sensor. Retest system.

Scheme 8

The PCM opens fuel injectors by grounding an injector driver circuit. PCM monitors voltage on each driver to detect a fault. If the voltage is not what the PCM expects to monitor (for example, due to an injector driver being shorted to voltage), a DTC will be set. Conditions required to set DTC are

1. Battery voltage is above 9 volts.
2. Engine is running.
3. Fuel pump is on.
4. When injector is commanded off, injector voltage is not equal to ignition voltage.
5. Listed conditions met for 5 seconds.

An open or short in injector driver circuit will cause a DTC P0201 to set and a misfire to occur due to inoperative injector. This type of DTC will indicate which cylinder is inoperative. Long and short term fuel trims being excessively high or low are a good indication that an injector is faulty.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Attempt to start engine. If engine starts, go to next step. If engine does not start, see ENGINE CRANKS BUT WILL NOT START under appropriate TROUBLE SHOOTING in «BASIC TESTING»(ref-16362) article.
3. Using scan tool, clear DTCs. Run engine at idle for one minute and check scan tool. If DTC P0201 has reset, go to step 5). If DTC P0201 has not set, go to next step.
4. Turn engine off. Turn ignition on. Using scan tool, read FREEZE FRAME data and note parameters. Operate vehicle within FREEZE FRAME conditions. If DTC P0201 is reset, go to next step. If no DTC is set, go to «DIAGNOSTIC AIDS»(ref-16367-S13889872982001010800000) .
5. Turn ignition off. Connect an Injector Test Light (J39021-45) to injector harness connector for cylinder No. 1. Disable secondary ignition system to prevent engine from starting, and crank engine. If test light flashes, perform fuel injector coil test. See FUEL SYSTEM in «SYSTEM & COMPONENT TESTS»(ref-16371) article. If test light does not flash, go to next step.
6. If injector test light was off or on steadily in previous step, go to next step. If test light was not off or on steadily in previous step, go to step 10).
7. Disconnect PCM connector from affected injectors. Using test light connected to battery positive, probe affected injectors driver circuit at harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
8. Repair short to ground in injector driver circuit. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article.
9. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article.
10. Disconnect harness connector from fuel injector. Turn ignition on. Connect test light to chassis ground and probe each terminal of injector harness connector (PCM side). If test light illuminates on Ignition (+) terminal only, go to step 12). If test light illuminates on other terminals including Ignition (+) terminal, go to next step.
11. Repair short to voltage in injector driver circuit. Retest system.
12. With test light still connected to ground, probe each terminal of injector harness connector (injector side). If test light illuminates on any terminal, go to step 11). If test light does not illuminate, go to next step.
13. Turn ignition off. Using an ohmmeter, check for an open between ignition terminal of injector harness connector (injector side) and each of the other terminals of injector harness connector (injector side). If all terminals have continuity, go to step 15). If any terminals were open, go to next step.
14. Repair open in injector drive circuit or injector. Retest system.
15. Check for an open in injector 1 control circuit between injector harness connector and PCM connector. If circuit is open, repair as necessary. Retest system. If circuit is okay, replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Attempt to start engine. If engine starts, go to next step. If engine does not start, see ENGINE CRANKS BUT WILL NOT START under appropriate TROUBLE SHOOTING in «BASIC TESTING»(ref-16362) article.
3. Using scan tool, clear DTCs. Run engine for one minute and check scan tool. If DTC P0202 has reset, go to step 5). If DTC P0202 has not set, go to next step.
4. Turn ignition on with engine off. Using scan tool, read FREEZE FRAME data and note parameters. Start engine and operate vehicle within FREEZE FRAME conditions. If DTC P0202 is reset, go to next step. If no DTC is set, go to «DIAGNOSTIC AIDS»(ref-16367-S14243989502001010800000) .
5. Turn engine off. Connect an Injector Test Light (J39021-45 ) to injector harness connector for cylinder No. 2. Disable secondary ignition system to prevent engine from starting, and crank engine. If test light flashes, perform fuel injector coil test. See FUEL SYSTEM in «SYSTEM & COMPONENT TESTS»(ref-16371) article. If test light does not flash, go to next step.
6. If test light was OFF or ON steadily in previous step, go to next step. If test light was not OFF or ON steadily in previous step, go to step 10).
7. Disconnect PCM connector from affected injectors. Using test light connected to battery positive, probe affected injectors driver circuit at harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
8. Repair short to ground in injector driver circuit. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article.
9. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article.
10. Disconnect harness connector from fuel injector(s). Turn ignition on. Connect test light to chassis ground and probe each terminal of injector harness connector (PCM side). If test light illuminates on Ignition (+) terminal only, go to step 12). If test light illuminates on other terminals including Ignition (+) terminal, go to next step.
11. Repair short to voltage in injector driver circuit. Retest system.
12. With test light still connected to ground, probe each terminal of injector harness connector (injector side). If test light illuminates on any terminal, go to step 11). If test light does not illuminate, go to next step.
13. Turn ignition off. Using an ohmmeter, check for an open between ignition terminal of injector harness connector (injector side) and each of the other terminals of injector harness connector (injector side). If all terminals have continuity, go to step 15). If any terminals were open, go to next step.
14. Repair open in injector drive circuit or injector. Retest system.
15. Check for an open in injector 2 control circuit between injector harness connector and PCM connector. If circuit is open, repair as necessary. Retest system. If circuit is okay, replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Attempt to start engine. If engine starts, go to next step. If engine does not start, see ENGINE CRANKS BUT WILL NOT RUN in «TESTS W/CODES - INTRODUCTION»(ref-16364) article.
3. Using scan tool, clear DTCs. Run engine for one minute and check scan tool. If DTC P0203 has reset, go to step 5). If DTC P0203 has not set, go to next step.
4. Turn ignition on with engine off. Using scan tool read FREEZE FRAME data and note parameters. Start engine and operate vehicle within FREEZE FRAME conditions. If DTC P0203 is reset, go to next step. If no DTC is set, go to «DIAGNOSTIC AIDS»(ref-16367-S06215624812001010800000) .
5. Turn engine off. Connect an Injector Test Light (J39021-45) to injector harness connector. Disable secondary ignition system to prevent engine from starting, and crank engine. If test light flashes, perform fuel injector coil test. See FUEL SYSTEM in «SYSTEM & COMPONENT TESTS»(ref-16371) article. If test light does not flash, go to next step.
6. If test light was off or on steadily in previous step, go to next step. If test light was not off or on steadily in previous step, go to step 10).
7. Disconnect PCM connector from affected injectors. Using test light connected to battery positive, probe affected injectors driver circuit at harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
8. Repair short to ground in injector driver circuit. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article.
9. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article.
10. Disconnect harness connector from fuel injector. Turn ignition on. Connect test light to chassis ground and probe each terminal of injector harness connector (PCM side). If test light illuminates on Ignition (+) terminal only, go to step 12). If test light illuminates on other terminals including Ignition (+) terminal, go to next step.
11. Repair short to voltage in injector driver circuit. Retest system.
12. With test light still connected to ground, probe each terminal of injector harness connector (injector side). If test light illuminates on any terminal, go to step 11). If test light does not illuminate, go to next step.
13. Turn ignition off. Using an ohmmeter, check for an open between ignition terminal of injector harness connector (injector side) and each of the other terminals of injector harness connector (injector side). If all terminals have continuity, go to step 15). If any terminals were open, go to next step.
14. Repair open in injector drive circuit or injector. Retest system.
15. Check for an open in injector 3 control circuit between injector harness connector and PCM connector. If circuit is open, repair as necessary. Retest system. If circuit is okay, replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Attempt to start engine. If engine starts, go to next step. If engine does not start, see ENGINE CRANKS BUT WILL NOT START under appropriate TROUBLE SHOOTING in «BASIC TESTING»(ref-16362) article.
3. Using scan tool, clear DTCs. Run engine for one minute and check scan tool. If DTC P0204 has reset, go to step 5). If DTC P0204 has not set, go to next step.
4. Turn ignition on with engine off. Using scan tool read FREEZE FRAME data and note parameters. Start engine and operate vehicle within FREEZE FRAME conditions. If DTC P0204 is reset, go to next step. If no DTC is set, go to «DIAGNOSTIC AIDS»(ref-16367-S19931688922001010800000) .
5. Turn engine off. Connect an Injector Test Light (J39021-45) to injector harness connector. Disable secondary ignition system to prevent engine from starting, and crank engine. If test light flashes, perform fuel injector coil test. See FUEL SYSTEM in «SYSTEM/COMPONENT TESTS»(ref-16371) article. If test light does not flash, go to next step.
6. If test light was OFF or ON steady in previous step, go to next step. If test light was not OFF or ON steady in previous step, go to step 10).
7. Disconnect PCM connector from affected injectors. Using test light connected to battery positive, probe affected injectors driver circuit at harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
8. Repair short to ground in injector driver circuit. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article.
9. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Perform On-Board II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article.
10. Disconnect harness connector from fuel injector. Turn ignition on. Connect test light to chassis ground and probe each terminal of injector harness connector (PCM side). If test light illuminates on Ignition (+) terminal only, go to step 12). If test light illuminates on other terminals including Ignition (+) terminal, go to next step.
11. Repair short to voltage in injector driver circuit. Retest system.
12. With test light still connected to ground, probe each terminal of injector harness connector (injector side). If test light illuminates on any terminal, go to step 11). If test light does not illuminate, go to next step.
13. Turn ignition off. Using an ohmmeter, check for an open between ignition terminal of injector harness connector (injector side) and each of the other terminals of injector harness connector (injector side). If all terminals have continuity go to step 15). If any terminals were open, go to next step.
14. Repair open in injector drive circuit or injector. Retest system.
15. Check for an open in injector 4 control circuit between injector harness connector and PCM connector. If circuit is open, repair as necessary. Retest system. If circuit is okay, replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

Scheme 9

Misfire is detected using Camshaft Position (CMP) and Crankshaft Position (CKP) sensors. When PCM senses CKP deceleration not associated with normal engine speed reduction, CMP is used to determine misfiring cylinder. PCM determines misfires on each cylinder, evaluates a random misfire and sets a DTC. Conditions required to set DTC are

1. No related DTCs set.
2. Engine speed is 600-6250 RPM.
3. System voltage is 11-16 volts.
4. ECT value is 20°F (7°C)-248°F (120°C).
5. Throttle angle is steady.
6. TP sensor reads less than 3.125%.
7. Vehicle speed is greater than 20 MPH.
8. Engine under a load.
9. PCM detects crankshaft RPM variation, indicating a misfire which could cause catalytic convertor damage or high emissions.

Using scan tool, read MISFIRE CUR # display for each cylinder. This will help locate and isolate which cylinder misfire is affecting. Check secondary ignition wires. Check for damaged or faulty ignition coil. Substitute a known-good ignition coil. Check system grounds. Check MAF sensor, air induction system, fuel pressure, injectors, and EGR valve.

Extended idle periods or short trip driving could leave deposits on HO2S. Deposits could cause HO2S to respond slowly, affecting fuel control and causing misfire at idle. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Start engine and allow it to idle. Using scan tool, read and record FREEZE FRAME data. Operate vehicle within conditions noted in FREEZE FRAME data. Using scan tool, read MISFIRE CUR # display for each cylinder. If MISFIRE CUR # is increasing (indicating a misfire currently occurring) for any cylinder, go to next step. If MISFIRE CUR # is not increasing, go to «DIAGNOSTIC AIDS»(ref-16367-S31543217762001010800000) .
3. Check vacuum hoses for splits, kinks, or improper connections. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
4. Check intake manifold, injector "O" rings, EGR valve, and EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Check PCV valve for improper installation or damaged hose. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
6. Inspect interior of distributor cap for carbon tracking. Check distributor rotor for damage. If a problem is found, repair as necessary. Retest system. If no problem was found, go to next step.
7. Remove ignition coils. Check ignition coils for cracks or carbon tracking. If a problem is found, replace damaged ignition coils. Retest system. If no problem is found, go to next step.
8. Remove EGR valve and inspect valve, seat and passages for damage. Inspect valve pintle to ensure it is not sticking partially open. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
9. Install a spark tester on spark plug wire at spark plug end for cylinder indicating most severe misfire. Crank engine and check for crisp, Blue spark at tester. Repeat procedure for each affected cylinder. If spark is okay on all cylinders, go to step 13). If spark is not okay on any cylinder, go to next step.
10. Remove spark plug(s) associated with misfiring cylinder(s). Check spark plugs for excessive fouling. If spark plugs are excessively fouled, diagnose and repair mechanical engine problem. If spark plugs are not excessively fouled, go to next step.
11. Check spark plug insulation for cracks, carbon tracking or other damage. If a problem is found, replace faulty spark plug(s). Retest system. If no problem is found, go to next step.
12. Replace ignition control module. Retest system.
13. Check PCM injector, power and sensor grounds for clean and tight connection, and for proper location. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
14. Perform a fuel pump pressure test. See FUEL SYSTEM in «BASIC TESTING»(ref-16362) article. If a problem was found, repair as necessary. Retest system. If no problem was found, go to next step.
15. Check for fuel contamination. If fuel is contaminated, repair condition causing contamination. Retest system. If fuel is okay, go to next step.
16. Perform FUEL INJECTOR BALANCE TEST under FUEL SYSTEM in «SYSTEM & COMPONENT TESTS»(ref-16371) article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
17. Diagnose mechanical engine problems such as faulty or incorrect camshaft, leaking valves or piston rings, sticky valves, excessive valve deposits, loose or worn rocker arms, weak valve springs, incorrect valve timing, leaking head gasket, or loose or broken motor mounts. If a problem is found, repair as necessary. Retest system.

Scheme 10

Knock sensor is used to detect engine detonation. Knock sensor produces and sends an AC voltage signal to the PCM to identify engine knock being detected. PCM will retard timing based on this signal.

Conditions required to set DTC are

1. Engine running time greater than 10 minutes.
2. DTC P0327 is not set.

Check for faulty connections or damaged harness. Correct any abnormal engine noises. Any audible noise that causes a knocking type noise on the engine block may be misinterpreted by knock sensor. Check for an open ignition feed. Scan tool will display knock sensor in counts, increasing with engine speed and decreasing when engine speed decreases. Check internal resistance of knock sensor to verify component or wiring type of problem in knock sensor circuit.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Start engine. Using scan tool, clear trouble codes. Run engine at slightly more than 10% throttle angle. If MIL illuminates, go to step 4). If MIL does not illuminate, go to next step.
3. Turn engine off. Turn ignition on. Review FREEZE FRAME data and note readings. Operate vehicle within conditions noted for setting DTC. If MIL illuminates, go to next step. If MIL does not illuminate, go to step 13).
4. Listen to engine while raising and lowering engine speed. If an abnormal audible noise is present, go to next step. If an abnormal audible engine noise is not present, go to step 6).
5. Repair cause of abnormal engine noise. Retest for DTC P0325.
6. While observing scan tool, slowly increase engine speed to 2500 RPM. If KS count increases with engine RPM, go to next step. If KS count does not increase with engine RPM, go to step 9).
7. Turn ignition off. Inspect PCM and KS connectors for damaged terminals. If connectors are okay, go to next step. If either connector needed repair, go to step 13).
8. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.
9. Turn ignition off. Disconnect PCM connectors. Using a DVOM connected to ground, measure resistance of KS through knock sensor circuit. If reading is 90-110 k/ohms, go to step 7). If reading is not as specified, go to next step.
10. Check knock sensor electrical connector for a poor connection and repair as necessary. If connector is okay, go to next step. If repair was necessary, go to step 13).
11. Check KS signal circuit for an open or shorted condition. Repair as necessary and go to step 13). If an open or shorted condition does not exist in KS circuit, go to next step.
12. Replace knock sensor. Go to next step.
13. Using scan tool, clear DTCs. Start engine and idle to normal operating temperature. Operate vehicle within conditions for setting DTC. If scan tool indicates this diagnostic has RAN AND PASSED, go to next step. If scan tool does not indicate this diagnostic has RAN AND PASSED, go to step 2).
14. Check for any additional DTCs. If additional DTCs are set, see appropriate DIAGNOSTIC TEST for DTC set. If no other DTCs exist, system is okay.

1. Perform ON-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Start engine. Using scan tool, operate vehicle within the conditions specified to set the DTC. Monitor specific DTC information for DTC P0327 until the P0327 test runs. Observe and record the test results. If scan tool indicates DTC P0327 FAILED THIS IGNITION, go to step 4). If scan tool does not indicate DTC P0327 FAILED THIS IGNITION, go to next step.
3. Turn engine off. Turn ignition on. Review and record FREEZE FRAME data and note readings. Operate vehicle within FAILURE RECORDS conditions. Monitor SPECIFIC DTC information for DTC P0327. Observe test results. If scan tool does not indicate DTC P0327 FAILED THIS IGNITION, go to DIAGNOSTIC AIDS. If scan tool indicates DTC P0327 FAILED THIS IGNITION, go to next step.
4. Turn ignition off. Disconnect KS. Turn ignition on. Using a DVOM, measure voltage between KS connector terminals. If reading is about 5 volts, go to next step. If reading is not about 5 volts, go to step 8).
5. Measure resistance of KS by connecting DVOM between KS terminal and engine block. If resistance is about 100 k/ohms, go to next step. If reading is not about 100 k/ohms, go to step 9).
6. Check KS sensor signal circuit for a poor terminal connection. If a problem was found, repair as necessary and go to next step. If connection is okay, go to step 9).
7. Connect KS. Turn ignition on. Using scan tool, monitor KS reading. Using a metal object, tap engine block. If KS value changes, go to step 11). If no change is indicated, go to next step.
8. Turn ignition off. Disconnect PCM. Turn ignition on. Check KS signal circuit for an open or shorted condition. Repair as necessary. If repair was performed, go to step 11). If open or shorted condition was not present, go to step 10).
9. Replace KS. Retest system.
10. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.
11. Using scan tool, select the DTC and clear information. Start engine. Idle engine to normal operating temperature. Select specific DTC. Enter DTC P0327. Operate the vehicle within the conditions for setting DTC P0327. If scan tool indicates vehicle RAN AND PASSED, system is okay. If scan tool indicates DTC FAILED THIS IGNITION, return to step 2).

1. Perform ON-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Attempt to start engine. If engine starts and runs, go to next step. If engine does not start and run, see ENGINE CRANKS BUT WILL NOT START under appropriate TROUBLE SHOOTING in «BASIC TESTING»(ref-16362) article.
3. Using scan tool, clear DTC P0336. Start engine and allow it to idle for one minute. Read DTCs. If DTC P0336 resets, go to next step. If DTC does not reset, go to «DIAGNOSTIC AIDS»(ref-16367-S33514994192001010800000) .
4. Disconnect PCM and CMP sensor connector. Check for an open or a short to ground in 58X reference circuit between CKP sensor connector and PCM harness connector. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Reconnect PCM and CKP sensor. Using a DVOM, measure voltage on 58X reference circuit at PCM connector while cranking engine. If DVOM reads around 2.5 volts, go to step 8). If voltage is not as specified, go to next step.
6. Check for faulty connections at CKP sensor. If a faulty connection is found, repair as necessary. Retest system. If connections are okay, go to next step.
7. Replace CKP sensor. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.
8. Check for faulty connections at PCM. If a faulty connection is found, repair as necessary. Retest system. If connections are okay, go to next step.
9. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition off and disconnect CKP sensor. Turn ignition on. Connect DVOM between 5-volt reference and sensor ground terminals at connector harness. If DVOM reads 5 volts, go to step 5). If reading is not as specified, go to next step.
3. With ignition on, use DVOM to backprobe PCM connector reference and ground terminals. If DVOM reads 5 volts, go to next step. If reading is not as specified, go to step 9).
4. Using DVOM, check resistance at reference and ground circuits at CKP harness connector. If an open or short is discovered, repair circuit. Retest system.
5. Turn ignition off and disconnect PCM and CKP sensor. Check for an open or a short in 58X reference circuit between CKP sensor connector and PCM harness connector. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
6. Connect PCM and CKP sensor. Using DVOM, measure voltage on 58X reference circuit at PCM connector and crank engine. If reading on DVOM is about 2.5 volts, go to step 9). If voltage is not as specified, go to next step.
7. Inspect connections at CKP sensor. Repair connections as necessary. Retest system. If connections did not require repair, go to next step.
8. Replace CKP sensor. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.
9. Inspect connections at PCM. Repair connections as necessary. Retest system. If connections did not require repair, go to next step.
10. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Using scan tool, read and record FAILURE RECORDS data for DTC P0341. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0341 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0341 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(ref-16367-S22451288652001010800000) .
3. Using DVOM, backprobe PCM connector at CMP signal circuit. With sensor connected, crank engine and monitor voltage. If voltage toggles 0-4 volts, go to next step. If voltage does not toggle 0-4 volts, go to step 6).
4. Check for poor connection at PCM connector terminal D11. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.
6. Disconnect CMP sensor. Turn ignition on. Measure voltage at CMP sensor harness connector between sensor feed circuit and sensor ground circuit. If reading is about battery voltage, go to step 11). If reading is not as specified, go to next step.
7. Measure voltage between CMP positive connector at CMP sensor harness connector and ground. If reading is about battery voltage, go to step 9). If reading is not as specified, go to next step.
8. Repair open between PCM main relay and CMP sensor. Retest system.
9. Measure voltage between battery positive and CMP ground wire at CMP sensor harness connector. If reading is around battery voltage, go to step 11). If reading is not as specified, go to next step.
10. Repair open in ground circuit. Retest system.
11. Turn ignition off. Using DVOM, check continuity of signal wire between CMP sensor and PCM. If continuity does not exist, repair open signal wire. Retest system. If continuity exists, go to next step.
12. Turn ignition on. Check signal wire for short to ground or short to voltage. If problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
13. Replace CMP sensor. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Using scan tool, read and record FAILURE RECORDS data for DTC P0342. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0342 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0342 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(ref-16367-S16152136002001010800000) .
3. Using DVOM, backprobe PCM connector at CMP signal circuit. With sensor connected, crank engine and monitor DVOM. If reading toggles 0-4 volts, go to next step. If reading does not toggle 0-4 volts, go to step 7).
4. Check for poor connection at PCM terminal D11. If a problem is found, repair as necessary. Retest system. If open or poor connection is not found, go to next step.
5. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.
6. Disconnect CMP sensor. Turn ignition on. Measure voltage at CMP sensor harness connector between sensor feed circuit and sensor ground circuit. If voltage is about battery voltage, go to step 11). If voltage is not as specified, go to next step.
7. Measure voltage between CMP positive connector at CMP sensor harness connector and ground. If reading is around battery voltage, go to step 9). If reading is not as specified, go to next step.
8. Repair open between PCM main relay and CMP sensor. Retest system.
9. Measure voltage between CMP positive connector and ground connector at CMP sensor harness connector. If reading is about battery voltage, go to step 11). If reading is not as specified, go to next step.
10. Repair open or short to ground. Retest system.
11. Turn ignition off. Using DVOM, check continuity of signal wire between CMP sensor and PCM. If continuity does not exist, repair open in signal wire. Retest system. If continuity exists, go to next step.
12. Turn ignition on. Check signal wire for short to ground or voltage. If problem is found, repair as necessary. Retest system. If no problem is found, replace CMP sensor. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

When the module receives a 5-volt signal from the PCM, it provides a ground path for the battery voltage supplied to the ignition primary coil. When the PCM turns off the 5 volts to the module, the module will remove the ground path of the ignition primary coil, causing the magnetic field produced by the coil to collapse. The PCM monitors the circuit and will set DTC P0351 if a problem in the ignition control circuit is detected.

Conditions required to set DTC are

1. Ignition is on.
2. Output voltage is not equal to 5 volts when output is on.
3. Output voltage is not equal to zero volts when output is off.
4. 20 test failures have occurred within 40 samples of continuous circuit monitoring.

Check for poor PCM connection or damaged harness. Inspect wiring harness for damage by observing scan tool while moving connector and wiring related to ignition system. A change in display will indicate location of fault. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Check ignition control module for poor connection or damaged terminals. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
3. Check PCM connector for poor connection or damaged terminals. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step. 4) Turn ignition off. Disconnect harness from PCM and ignition control module. Check ignition control circuit for an open or shorted condition. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step. 5) Replace ignition control module. Retest system. If problem still exists, go to next step.
4. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

When the module receives a 5-volt signal from the PCM, it provides a ground path for the battery voltage supplied to the ignition primary coil. When the PCM turns off the 5 volts to the module, the module will remove the ground path of the ignition primary coil, causing the magnetic field produced by the coil to collapse. The PCM monitors the circuit and will set DTC P0352 if a problem in the ignition control circuit is detected.

Conditions required to set DTC are

1. Ignition is on.
2. Output voltage is not equal to 5 volts when output is on.
3. Output voltage is not equal to zero volts when output is off.
4. 20 test failures have occurred within 40 samples of continuous circuit monitoring.

Check for poor PCM connection or damaged harness. Inspect wiring harness for damage by observing scan tool while moving connector and wiring related to ignition system. A change in display will indicate location of fault. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Check ignition control module for poor connection or damaged terminals. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
3. Check PCM connector for poor connection or damaged terminals. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step. 4) Turn ignition off. Disconnect harness from PCM and ignition control module. Check ignition control circuit for an open or shorted condition. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step. 5) Replace ignition control module. Retest system. If problem still exists, go to next step.
4. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

Scheme 11

PCM tests Exhaust Gas Recirculation (EGR) valve during deceleration by momentarily commanding EGR valve on while monitoring engine MAP. PCM will illuminate MIL and store DTC P0401 if expected increase in MAP is not seen under test conditions during deceleration.

Conditions required to set DTC are

1. No ECT, EVAP, IAC, IAT, MAP, TP or VSS DTCs set.
2. BARO is greater than 75 kPa.
3. ECT is greater than 140°F (60°C).
4. IAC position is steady, changing less than 5 counts.
5. System voltage is 11.5-16 volts.
6. Vehicle speed greater than 15 MPH.
7. Commanded state of A/C relay is steady.

PCM will only run EGR flow test during gradual deceleration, a closed throttle condition and with vehicle speed greater than 20 MPH. Accelerate vehicle to greater than 20 MPH, and gradually decelerate 9-13 times. Check for faulty connections or damaged harness. Inspect PCM harness connector EGR control circuit for backed-out terminal. Observe ACTUAL EGR POSITION display on scan tool while moving all related harnesses and connectors. A change in scan tool display indicates fault location.

If EGR valve shows signs of excessive heat, check exhaust system for blockage or plugged catalytic converter. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Start engine and allow it to idle. Using scan tool, monitor MAP signal. Jab accelerator pedal halfway and release quickly, returning to idle. If scan tool showed immediate large change in MAP value, go to next step. If scan tool did not show immediate large change in MAP value, replace MAP sensor. Retest system.
3. Inspect exhaust system for modifications or leaks. If a problem is found, repair as necessary and go to step 6). If no problem is found, go to next step.
4. Remove EGR valve and check pintle, valve and passages and adapter for excessive deposits or restriction. Check EGR valve gasket and pipes for leaks. If a problem is found, repair as necessary and go to step 6). If no problem is found, go to next step.
5. Remove EGR inlet and outlet pipes from exhaust and intake manifolds. Inspect manifold EGR ports and pipes for blockage or damage. If a problem is found, repair as necessary and go to next step. If no problem is found, see «DIAGNOSTIC AIDS»(ref-16367-S33707581662001010800000) .
6. Read and record FAILURE RECORDS data for DTC P0401. Clear DTCs and monitor EGR TEST COUNT while operating vehicle within conditions noted in DIAGNOSTIC AIDS. Read SPECIFIC DTC. If scan tool displays DTC P0401 TEST RAN AND PASSED, repair is complete. If scan tool does not display DTC P0401 TEST RAN AND PASSED, return to step 2).

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle as specified in DIAGNOSTIC AIDS. Using scan tool, monitor SPECIFIC DTC information for DTC P0402. If scan tool displays DTC P0402 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0402 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(ref-16367-S29118001442001010800000) .
3. Inspect exhaust system for modification of original installed parts or leaks. Repair as necessary. If exhaust system is okay, go to next step.
4. Remove EGR valve and check pintle, valve, passages and adapter for excessive deposits or restriction. Check EGR valve gasket and pipes for leaks. If a problem is found, repair as necessary. If no problem is found, go to next step.
5. Remove EGR inlet and outlet pipes from the exhaust manifold and intake manifold. Inspect manifold EGR ports and pipes for damage, restriction or blockage. Repair or replace as necessary. If repair is not needed, see «DIAGNOSTIC AIDS»(ref-16367-S29118001442001010800000) .

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Command EGR valve to 25%, 50%, 75% and 100%, while observing EGR valve position. If actual EGR valve position follows the desired EGR position, go to step 19). If EGR actual position is different than EGR desired position, go to next step.
3. Turn ignition off. Disconnect EGR valve harness connector. Turn ignition on. Using a test light connected to battery voltage, probe EGR ground circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 5).
4. Using a test light connected to ground, probe EGR control circuit. Using scan tool, command EGR valve percentage to increase (25%, 50%, 75% and 100%). If test light illuminates brighter, flashes or maintains a steady glow with each increase command, go to step 6). If test light does not illuminate brighter, flash or maintain a steady glow for each increase command, go to step 7).
5. Repair open or poor connection in EGR ground circuit as necessary. Go to step 19).
6. Using test light connected to ground, probe EGR signal circuit. If test light illuminates, go to step 8). If test light does not illuminate, go to step 9).
7. Using test light connected to ground, probe EGR control circuit. If test light illuminates, go to step 10). If test light does not illuminate, go to step 11).
8. Check EGR signal circuit for short to voltage. Repair as necessary. Go to step 19). If short to voltage does not exist, go to step 12).
9. Using a DVOM connected to ground, probe EGR 5-volt reference circuit terminal. If reading is about 5 volts, go to step 13). If reading is not about 5 volts, go to step 14).
10. Check EGR control circuit for short to voltage. Repair as necessary. Go to step 19). If short to voltage does not exist, go to step 12).
11. Using a test light connected to battery voltage, probe EGR control circuit. If test light illuminates, go to step 15). If test light does not illuminate, go to step 16).
12. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Go to step 19).
13. Check EGR ground circuit for poor connection at PCM harness connector. Repair as necessary. Go to step 19). If connection is okay, go to step 17).
14. Check EGR 5-volt reference circuit for a short to voltage. Repair as necessary. Go to step 19). If short to voltage does not exist, go to step 12).
15. Check EGR control circuit for a short to ground. Repair as necessary. Go to step 19). If short does not exist, go to step 12).
16. Check EGR control circuit for an open or poor connection at EGR valve harness connector. Repair as necessary. Go to step 19). If an open or poor connection does not exist, go to step 18).
17. Replace EGR valve. Go to step 19).
18. Check PCM harness connectors for poor connection. Repair as necessary. Go to next step.
19. Using scan tool, clear DTCs. Start engine and idle to normal operating temperature. Operate vehicle within conditions for setting DTC P0404. See Circuit Description. If scan tool indicates diagnostic RAN AND PASSED, system is okay. If scan tool indicates diagnostic did not pass, go to step 2).

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Command EGR valve to 25%, 50%, 75% and 100%, while observing EGR valve position. If actual EGR valve position follows the desired EGR position, go to step 15). If EGR actual position is different than EGR desired position, go to next step.
3. Using a DVOM connected to ground, probe EGR 5-volt reference circuit. If reading is about 5 volts, go to step 4). If reading is not about 5 volts, go to step 5).
4. Turn ignition off. Using a jumper wire, connect EGR valve harness connector 5-volt reference circuit to signal circuit. Turn ignition on. If actual EGR position reading on scan tool is 100%, go to step 6). If actual EGR position reading is not 100%, go to step 7).
5. Using a test light connected to battery voltage, probe EGR 5-volt reference circuit. If test light illuminates, go to step 8). If test light does not illuminate, go to step 9).
6. Check EGR 5-volt reference circuit and signal circuit for poor connection at PCM and EGR valve harness connectors. Repair as necessary. Go to step 15). If all connectors are okay, go to step 10).
7. Using a test light connected to battery voltage, probe EGR signal circuit. If test light illuminates, go to step 11). If test light does not illuminate, go to step 12).
8. Check for short to ground in EGR 5-volt reference circuit. Repair as necessary and go to step 15). If short does not exist, go to step 13).
9. Check for an open in EGR 5-volt reference circuit. Repair as necessary, and go to step 15). If an open does not exist, go to step 14).
10. Replace EGR valve. Go to step 15).
11. Check for short to ground in EGR signal circuit. Repair as necessary, go to step 15). If short does not exist, go to step 13).
12. Check for an open in EGR signal circuit. Repair as necessary, go to step 15). If an open does not exist, go to next step.
13. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Go to step 15).
14. Turn ignition off. Disconnect PCM harness connectors. Check for poor connections at EGR valve circuit terminals of PCM and PCM harness connector. Repair as necessary, go to next step. If PCM and PCM harness connector terminals are okay, go to step 13).
15. Using scan tool, clear DTCs. Start engine and idle to normal operating temperature. Operate vehicle within conditions for setting DTC P0405. See Circuit Description. If scan tool indicates diagnostic RAN AND PASSED, system is okay. If scan tool indicates diagnostic did not pass, go to step 2).

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Using scan tool, read and record FAILURE RECORDS data for DTC P0406. Clear DTC from PCM memory. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0406 RAN AND PASSED, see «DIAGNOSTIC AIDS»(ref-16367-S26031343632001010800000) . If scan tool does not display DTC P0406 RAN AND PASSED, go to next step.
3. Turn ignition off. Disconnect EGR valve harness connector. Turn ignition on. Using DVOM, check for voltage at ignition feed circuit terminal of EGR valve harness connector. If reading is about 12 volts, go to step 5). If reading is not about 12 volts, go to next step.
4. Check for an open or shorted condition in the ignition feed circuit. Ensure ENGINE IG (15-amp) fuse is okay. Repair as necessary. Retest system. If an open or shorted condition does not exist, go to step 7).
5. Using DVOM, check resistance of the EGR solenoid. If reading is less than 5 ohms, go to next step. If reading is greater than 5 ohms, go to step 14).
6. Check EGR solenoid valve low circuit between EGR valve and PCM for an open or shorted condition. Repair as necessary. Retest system. If an open or shorted condition does not exist, go to step 15).
7. Turn ignition off. Disconnect EGR valve harness connector. Turn ignition on. Observe EGR value on scan tool. If reading is zero volts and zero percent, go to step 9). If reading is not as specified, go to next step.
8. Check EGR position feedback circuit between EGR sensor and PCM for an open or shorted condition. Repair as necessary. Retest system. If an open or shorted condition does not exist, go to step 15).
9. Using DVOM, check for voltage on EGR 5-volt reference circuit at EGR harness connector. If reading is about 5 volts, go to step 11). If reading is not about 5 volts, go to next step.
10. Check EGR valve 5-volt reference circuit between EGR valve and PCM for an open or shorted condition. Repair as necessary. Retest system. If an open or shorted condition does not exist, go to next step.
11. Turn ignition off. Connect DVOM between 5-volt reference circuit and ground circuit terminals of EGR valve harness connector. Turn ignition on. If reading is about 5 volts, go to step 13). If reading is not about 5 volts, go to next step.
12. Check EGR ground circuit for an open or shorted condition. Repair as necessary. Retest system. If ground circuit is okay, go to step 15).
13. Turn ignition off. Using a fused jumper wire, connect 5-volt reference circuit and EGR feedback circuit terminals of EGR valve harness connector. Turn ignition on. Observe EGR value on scan tool. If reading is 5 volts and 100%, go to next step. If value is not as specified, go to step 15).
14. Replace EGR valve. Retest system.
15. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Go to step 15).

Three-Way Catalyst (TWC) system is used to control emission. PCM uses signal from Heated Oxygen Sensors (HO2S) to read efficiency of TWC. PCM will set DTC P0420 if TWC oxygen storage capacity is less than a predetermined threshold.

Conditions required to set DTC are

1. No related DTCs set.
2. Engine is operating in closed loop.
3. Engine air load is below 99.6%.
4. ECT is above 140°F (60°C).
5. MAF calculated airflow is 10-32 grams/second.
6. Change in engine load is below 3.91%.
7. Catalyst temperature is above 750°F (399°C).
8. Engine speed below 3500 RPM.
9. Vehicle speed is 15-75 MPH.
10. PCM determines catalysts oxygen storage capacity less than predetermined threshold.

Check for faulty connections or damaged harness. Inspect PCM harness connector EGR control circuit for backed-out terminal. Observe scan tool while moving all related harnesses and connectors. A change in scan tool display indicates fault location.

Ensure engine has reached operating temperature. Place gear selector in Park. Using scan tool, monitor HO2S-1 and HO2S-2 values while using scan tool IAC RPM function to maintain MAF at 10 grams per second. Compare activity between HO2S-1 and HO2S-2 for 30 seconds. If activity between both HO2S is about equal, a problem exists. Repeat DTC P0420. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Diagnose any other HO2S DTC(s) set before proceeding. If no other HO2S DTC are set, go to next step.
3. Ensure TWC is an original equipment part. Check TWC for dents, or discoloration caused by excessive heat. Ensure no internal damage or catalyst rattle exists. If a problem is found, repair as necessary and go to step 6). If no problems are found, go to next step.
4. Check exhaust system for leaks, damage, loose or missing hardware. If a problem is found, repair as necessary and go to step 7). If no problems are found, go to next step.
5. Ensure HO2S-2 is securely installed and that harness is not damaged or contacting exhaust. If a problem is found, repair as necessary and go to step 7). If no problems are found, go to next step.
6. Replace TWC. Check for possible engine misfire DTC or engine mechanical problem, and go to next step.
7. Read and record FAILURE RECORDS data for DTC P0420. Clear DTCs. Start engine and allow it to be greater than 140°F (60°C). Run engine (while monitoring scan tool IAC RPM control function) to maintain MAF at 7-41 grams per second for at least 2 minutes. Using scan tool, monitor TWC MONITOR TEST COUNTER while operating vehicle within conditions required to set DTC. Continue operating vehicle until TWC MONITOR TEST COUNTER reaches 49 and returns to zero 2 times. Read SPECIFIC DTC. If scan tool displays DTC P0420 TEST RAN AND PASSED, repair is complete. If scan tool does not display DTC P0420 TEST RAN AND PASSED, return to step 2).

Scheme 12

Note. EVAP Diagnostic Station (P/N J41413), or similar, is necessary for accurate diagnostics of EVAP system. This tool will be necessary for vacuum and pressurized leakdown testing of EVAP systems. It is equipped with 2 additional gauges to measure vacuum in inches of mercury (in. Hg), and to measure vapor flow in inches of water (in. H2O), within an EVAP circuit.

Evaporative (EVAP) emission system is checked by applying vacuum to the EVAP system and monitoring for a vacuum leak. PCM monitors vacuum level via fuel tank pressure sensor signal. When appropriate, EVAP canister purge valve and EVAP canister vent solenoid are turned on, allowing engine to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, EVAP canister purge valve is turned off, sealing the EVAP system. If a large leak is detected, DTC P0440 will be set under the following conditions.

Conditions required to set DTC are

1. DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134 and P1133 are not set.
2. BARO is greater than 72.3 kPa.
3. Start-up IAT and ECT is greater than 38°F (3.5°C).
4. Difference between ECT and IAT at start up is less than 12.2°F (6.75°C).
5. Vehicle speed is less than 60 MPH.
6. Fuel tank level sensor reads 10-90%.
7. Fuel counts vary by less than 15 counts in .125 second time frame.
8. Maximum engine run time is at least 540 seconds (9 min.).
9. Difference between the actual fuel tank pressure and the expected fuel tank pressure is less than the PCM's expectations.

The above conditions are met, and the following is met once

1. EVAP system is unable to maintain vacuum, depending upon amount of fuel in fuel tank, during diagnostic test.

Check gas cap, vacuum canister and EVAP hoses, lines and EVAP components for damage. Check for faulty connections or damaged harness. Observe EVAP system components displayed on scan tool while moving all related harnesses and connectors. A change in scan tool display indicates fault location. If DTC cannot be duplicated, check scan tool FAILURE RECORDS and FREEZE FRAME data to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Diagnose DTC P0461, P0462 or P0463, if set. See appropriate testing procedure under DIAGNOSTIC TESTS. If specified DTCs are not set, go to next step.
3. Perform a visual and physical inspection of fuel cap. Replace as necessary. Retest system. If fuel cap is in good condition and properly installed, go to next step.
4. Using scan tool, command EVAP canister purge control valve and vent solenoid on and off. Ensure purge valve and vent solenoid make a click when commanded on and off with scan tool. If click is heard, go to next step. If no click is heard, inspect components and verify PCM output signal to each component.
5. Turn ignition off. Remove fuel cap. Turn ignition on. Using scan tool, read fuel tank pressure value. If reading is 0 IN. (+/- 1 in.) H2O, go to step 8). If reading is not as specified, go to next step.
6. If battery has been disconnected, perform a visual and physical inspection of EVAP system. Repair as necessary. Record and clear DTCs from memory. Test drive vehicle. Refer to test procedures for any DTC(s) set. If no DTC sets, problem may be an intermittent condition. If battery was not disconnected, go to next step.
7. Disconnect battery. Wait at least 20 seconds, and reconnect battery. Go to step 5). NOTE: Calibrate EVAP pressure/vacuum gauges before proceeding. See manufacturer's operating instructions.
8. Install fuel cap. Using scan tool, command the EVAP vent solenoid ON (closed). Connect EVAP pressure/vacuum gauge to EVAP service port. Attempt to pressurize the EVAP system to 5 in. H2O. If 5 in. H2O pressure can be achieved, go to next step. If 5 in. H2O pressure cannot be achieved, go to step 10).
9. If fuel tank pressure maintains 5 in. (+/- 2 in.) H2O, go to step 12). If pressure cannot be maintained, go to step 11).
10. Disconnect fuel tank vapor line and EVAP purge line from EVAP canister. Block canister fitting for the fuel tank vapor line. Connect a hand vacuum pump to the canister fitting for the EVAP purge line. Ensure EVAP vent solenoid is still commanded ON (closed). Apply 5 in. Hg to EVAP canister. If vacuum can be maintained, go to step 15). If vacuum cannot not be maintained, go to step 14).
11. Perform a visual and physical inspection of EVAP system. Check for restricted fuel tank vapor line. Check for a restricted EVAP purge line. Repair as necessary. Retest system. If no problems are found, perform a visual and physical inspection of entire EVAP system. Repair as necessary. Record and clear DTCs from memory. Test drive vehicle. Refer to test procedures for any DTC(s) set. If no DTC sets, problem may be an intermittent condition. 12) Disconnect vacuum line from between throttle body and EVAP canister. Connect hand vacuum to EVAP canister purge valve vacuum source. Apply 10 in. HG to EVAP canister purge valve. Using scan tool, command EVAP purge valve ON. If vacuum is released, go to next step. If vacuum is not released, go to step 17).
12. Connect pressure/vacuum gauge to vacuum source line. Start engine and hold at 2500 RPM. While observing vacuum gauge, jab accelerator pedal and allow engine to return to idle. If vacuum gauge reads greater than 10 in. Hg when throttle was opened and closed, go to «DIAGNOSTIC AIDS»(ref-16367-S11556196032001010800000) . If reading was not as specified, go to step 18).
13. Perform a visual and physical inspection of EVAP system. Repair any damaged EVAP components as necessary. Retest system. If EVAP system components are okay, go to step 19).
14. Perform a visual and physical inspection of EVAP system. Check for missing, damaged or defective gas cap, vapor lines or EVAP purge line. Repair as necessary. Retest system. If inspection is okay, go to next step.
15. Using scan tool, command EVAP vent solenoid ON. Attempt to pressurize the EVAP system, while locating leak with ultrasonic leak detector. Repair as necessary. Go to step 20).
16. Replace EVAP canister purge valve. Go to step 20).
17. Repair the cause of no source vacuum to EVAP canister purge valve. Go to step 20).
18. Replace EVAP vent solenoid. Go to step 20). NOTE: Review temperature variation instructions included with EVAP Diagnostic Station pressure and vacuum gauge operating instructions before proceeding.
19. Turn ignition on. Using scan tool, command the EVAP vent solenoid ON (closed). Connect EVAP pressure/vacuum gauge to EVAP service port. Attempt to pressurize the EVAP system to 15 in. H2O. If 15 in. H2O pressure can be achieved and held for 2 minutes, system is okay. If pressure cannot be held, go to step 3).

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Diagnose DTC P0461, P0462 or P0463, if set. See appropriate DIAGNOSTIC TESTS. If specified DTCs are not set, go to next step.
3. Using scan tool, command EVAP canister purge control valve and vent solenoid on and off. Ensure purge valve and vent solenoid make a click when commanded on and off with scan tool. If click is heard, go to next step. If no click is heard, inspect components and verify PCM output signal to each component. See «PIN VOLTAGE CHARTS»(ref-16370) article.
4. Turn ignition off. Remove fuel cap. Turn ignition on. Using scan tool, read fuel tank pressure value. If reading is 0 IN. H2O (+/- 1 in. H2O), go to step 7). If reading is not as specified, go to next step.
5. If battery has been disconnected, perform a visual and physical inspection of EVAP system. Repair as necessary. Record and clear DTCs from memory. Test drive vehicle. Refer to test procedures for any DTC(s) set. If no DTC sets, problem may be an intermittent condition. If battery was not disconnected, go to next step.
6. Disconnect battery. Wait at least 20 seconds. Reconnect battery and go to step 4). NOTE: Calibrate EVAP pressure/vacuum gauges before proceeding. See manufacturer's operating instructions.
7. Install fuel cap. Using scan tool, command the EVAP vent solenoid ON (closed). Connect EVAP pressure/vacuum gauge to EVAP service port. Attempt to pressurize the EVAP system to 5 in. H2O. If 5 in. H2O pressure can be achieved, go to next step. If 5 in. H2O pressure cannot be achieved, go to step 14). NOTE: Review temperature variation instructions included with EVAP Diagnostic Station pressure and vacuum gauge operating instructions before proceeding.
8. Turn ignition on. Using scan tool, command EVAP vent solenoid on (closed). Using EVAP pressure/vacuum gauge, pressurize EVAP system to 15 in. H2O and hold pressure on system for 2 minutes. If pressure decrease to less than 15 in H2O, go to next step. If pressure does not decrease to less than 15 in. H2O, see «DIAGNOSTIC AIDS»(ref-16367-S02159097482001010800000) .
9. Disconnect fuel tank vapor line and EVAP purge line from EVAP canister. Block canister fitting for the fuel tank vapor line. Connect a hand vacuum pump to the canister fitting for the EVAP purge line. Ensure EVAP vent solenoid is still commanded ON (closed). Apply 5 in. Hg to EVAP canister. If vacuum can be maintained, go to step 12). If vacuum cannot be maintained, go to next step.
10. Perform a visual and physical inspection of EVAP system. Check for damaged or restricted fuel tank vapor lines or hoses and EVAP canister. Repair as necessary. Retest system. If no problems are found, go to next step.
11. Replace EVAP vent solenoid. Retest system.
12. Perform a visual and physical inspection of EVAP system. Check for missing, damaged or defective gas cap, vapor lines or EVAP purge line. Repair as necessary. Retest system. If inspection is okay, go to next step.
13. Using scan tool, command EVAP vent solenoid ON. Using EVAP pressure/vacuum gauge, pressurize the EVAP system while locating leak with ultrasonic leak detector. Repair as necessary.
14. Turn ignition on. Using scan tool, command the EVAP vent solenoid ON (closed). Connect EVAP pressure/vacuum gauge to EVAP service port. Attempt to pressurize the EVAP system to 15 in. Hg. If 15 in. Hg pressure can be achieved and held for 2 minutes, system is okay. If pressure cannot be held, go to step 3).

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on with engine off. Using scan tool read failure records FREEZE FRAME data and note parameters. Clear DTCs set. Start engine and operate vehicle within failure records FREEZE FRAME data conditions. If DTC P0443 is reset, go to next step. If no DTC is set, go to «DIAGNOSTIC AIDS»(ref-16367-S23518557952001010800000) .
3. Turn engine off. Disconnect EVAP canister purge control solenoid. Turn ignition on. Using a DVOM, check ignition feed circuit to EVAP canister purge control solenoid harness connector. If reading indicates 12 volts, go to step 5). If reading does not indicate 12 volts, go to next step.
4. Check for an open ENGINE IG (15-amp) fuse, located in instrument panel fuse block. Also, check for an open or short in circuit between ENGINE IG (15-amp) fuse and EVAP canister purge control solenoid harness connector. Repair as necessary. Retest system.
5. Using DVOM, measure resistance of EVAP canister purge control solenoid. If reading is less than 5 ohms, go to next step. If reading is greater than 5 ohms, go to step 7).
6. Turn ignition off. Disconnect PCM connectors. Check EVAP canister purge control solenoid circuit between PCM and harness connector for an open or shorted condition. Repair as necessary. If circuit is okay, go to step 8).
7. Replace EVAP canister purge control solenoid. Retest system.
8. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Diagnose DTC P0461, P0462 or P0463, if set. See appropriate DIAGNOSTIC TESTS. If specified DTCs are not set, go to next step.
3. Using scan tool, command EVAP canister purge control valve and vent solenoid on and off. Ensure purge valve and vent solenoid make a click when commanded on and off with scan tool. If click is heard, go to next step. If no click is heard, inspect components and verify PCM output signal to each component. See «PIN VOLTAGE CHARTS»(ref-16370) article.
4. Turn ignition off. Remove fuel cap. Turn ignition on. Using scan tool, read fuel tank pressure value. If reading is 0 IN. H2O (+/- 1 in. H2O), go to step 7). If reading is not as specified, go to next step.
5. If battery has been disconnected, perform a visual and physical inspection of EVAP system. Repair as necessary. Record and clear DTCs from memory. Test drive vehicle. Refer to test procedures for any DTC(s) set. If no DTC sets, problem may be an intermittent condition. If battery was not disconnected, go to next step.
6. Disconnect battery. Wait at least 20 seconds. Reconnect battery and go to step 4). NOTE: Calibrate EVAP pressure/vacuum gauges before proceeding. See manufacturer's operating instructions.
7. Install fuel cap. Using scan tool, command the EVAP vent solenoid ON (closed). Connect EVAP pressure/vacuum gauge to EVAP service port. Attempt to pressurize the EVAP system to 5 in. H2O. If 5 in. H2O pressure can be achieved, go to next step. If 5 in. H2O pressure cannot be achieved, locate leak in EVAP system using a leak detector. NOTE: Review temperature variation instructions included with EVAP Diagnostic Station pressure and vacuum gauge operating instructions before proceeding.
8. Maintain specified EVAP pressure. Using scan tool, command EVAP vent solenoid off (open) while observing pressure/vacuum gauge. If EVAP system returns to 5 in. H2O within 5 seconds, refer to «DIAGNOSTIC AIDS»(ref-16367-S40385139712001010800000) . If reading does not return as specified, go to next step.
9. Disconnect the large vent hose (marked AIR) from EVAP canister. Switch EVAP Diagnostic Station to purge function. Start engine and bring to normal operating temperature. While holding engine at 2500 RPM, observe diagnostic Station vacuum gauge for 5 seconds. If reading remains below 30 in. H2O, go to next step. If reading is not as specified, go to step 12).
10. Inspect EVAP vent hose between EVAP canister and EVAP vent solenoid for kinks, binding or a restriction. If such condition is found, repair as necessary and go to step 13). If vent hose is okay, go to next step.
11. Replace EVAP vent solenoid. Go to step 13).
12. Replace EVAP canister. Go to step 13).
13. Using scan tool, command EVAP vent solenoid ON (closed). Using EVAP Diagnostic Station pressurize EVAP system to 5 in. H2O. Place EVAP Diagnostic Station to HOLD position. While observing pressure gauge of EVAP Diagnostic Station, command EVAP vent solenoid OFF (open). IF the EVAP system pressure returns to 5 in. H2O within 5 seconds, system is okay. If EVAP system will not return to 5 in H2O, go to step 3).

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on with engine off. Using scan tool read failure records FREEZE FRAME data and note parameters. Clear DTCs set. Start engine and operate vehicle within failure records FREEZE FRAME data conditions. If DTC P0449 is reset, go to next step. If no DTC is set, go to «DIAGNOSTIC AIDS»(ref-16367-S00829803572001010800000) .
3. Turn engine off. Disconnect EVAP canister vent solenoid. Turn ignition on. Using a DVOM, check ignition feed circuit to EVAP canister purge control solenoid harness connector. If reading indicates 12 volts, go to step 5). If reading does not indicate 12 volts, go to next step.
4. Check for an open ENGINE IG (15-amp) fuse, located in instrument panel fuse block. Also, check for an open or short in circuit between ENGINE IG (15-amp) fuse and EVAP canister vent solenoid harness connector. Repair as necessary. Retest system.
5. Using DVOM, measure resistance of EVAP canister vent solenoid. If reading is less than 5 ohms, go to next step. If reading is greater than 5 ohms, go to step 7).
6. Turn ignition off. Disconnect PCM connectors. Check EVAP vent solenoid control circuit between PCM and harness connector for an open or shorted condition. Repair as necessary. If circuit is okay, go to step 8).
7. Replace EVAP canister vent solenoid. Retest system.
8. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on with engine off. Using scan tool read failure records FREEZE FRAME data and note parameters. Clear DTCs set. Start engine and operate vehicle within failure records FREEZE FRAME data conditions. If DTC P0452 is reset, go to next step. If no DTC is set, go to «DIAGNOSTIC AIDS»(ref-16367-S03544892662001010800000) .
3. Turn engine off. Disconnect Fuel Tank Pressure (FTP) sensor. Turn ignition on. Using a DVOM, check 5-volt reference circuit to FTP sensor harness connector and chassis ground. If reading indicates 4-6 volts, go to next step. If reading does not indicate 4-6 volts, go to step 5).
4. Check voltage reading between 5-volt reference and ground circuit terminals of FTP harness connector. Repair as necessary. Retest system.
5. Turn ignition off. Disconnect PCM harness connectors. Check 5-volt reference circuit for an open or shorted condition. Repair as necessary and retest system. If an open or shorted condition does not exist, go to next step.
6. Turn ignition off. Disconnect PCM harness connectors. Check FTP sensor input circuit for an open or shorted condition. Repair as necessary and retest system. If an open or shorted condition does not exist, go to step 8).
7. Turn ignition off. Disconnect PCM harness connectors. Check FTP sensor ground circuit for an open or shorted condition. Repair as necessary and retest system. If an open or shorted condition does not exist, go to step 9).
8. Replace FTP sensor. Retest system.
9. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on with engine off. Using scan tool read failure records FREEZE FRAME data and note parameters. Clear DTCs set. Start engine and operate vehicle within failure records FREEZE FRAME data conditions. If DTC P0453 is reset, go to next step. If no DTC is set, go to Diagnostic Aids.
3. Turn engine off. Disconnect Fuel Tank Pressure (FTP) sensor. Turn ignition on. Using a DVOM, check 5-volt reference circuit to FTP sensor harness connector and chassis ground. If reading indicates 4-6 volts, go to next step. If reading does not indicate 4-6 volts, go to step 5).
4. Check voltage reading between 5-volt reference and ground circuit terminals of FTP harness connector. Repair as necessary. Retest system.
5. Turn ignition off. Disconnect PCM harness connectors. Check 5-volt reference circuit for an open or shorted condition. Repair as necessary and retest system. If an open or shorted condition does not exist, go to next step.
6. Turn ignition off. Disconnect PCM harness connectors. Check FTP sensor input circuit for an open or shorted condition. Repair as necessary and retest system. If an open or shorted condition does not exist, go to step 8).
7. Turn ignition off. Disconnect PCM harness connectors. Check FTP sensor ground circuit for an open or shorted condition. Repair as necessary and retest system. If an open or shorted condition does not exist, go to step 9).
8. Replace FTP sensor. Retest system.
9. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

Scheme 13

PCM monitors fuel level sensor is an important input to the PCM for enhanced evaporative system diagnostic. PCM needs fuel level information for determining volume of fuel in the tank. Enhanced evaporative system diagnostic test needs fuel level input to gauge the rate of change in air pressure in the EVAP system. Enhanced evaporative system diagnostic test will not be performed when fuel level is greater than 85% or less than 15%.

Conditions required for setting DTC are

1. Fuel tank level slosh test is completed.
2. Tank level main test is completed.
3. Fuel tank level data is valid.
4. Fuel level signal changes by less than 7 counts (.14 volts) over a distance of 146 miles.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Compare fuel level reading on scan tool with vehicle fuel gauge. If readings are about the same, go to next step. If readings are not about the same, go to step 5).
3. Record fuel gauge reading. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. If vehicle fuel gauge reading changes, go to next step. If fuel gauge reading does not change, go to step 5).
4. Turn ignition off. Disconnect fuel tank level sensor connector. Using a fused jumper wire, jumper fuel level input to fuel level sensor ground. Turn ignition on. If the scan tool and fuel gauge indicate 0% (empty), go to next step. If scan tool and fuel gauge readings do not indicate 0%, go to step 6).
5. Replace fuel tank level sensor. Go to step 7).
6. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.
7. Using scan tool, clear DTC information. Start engine and idle to normal operating temperature. Operate the vehicle within the conditions for setting DTC P0461. If scan tool indicates diagnostic RAN AND PASSED, system is okay. If DTC does not indicate system passed, go to step 2).

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Observe fuel level reading on scan tool. If reading displayed is 0-1%, go to step 4). If scan tool does not indicate specified amount, go to next step.
3. Test fuel gauge operation. See «INSTRUMENT PANEL»(ref-26406) article in ACCESSORIES/SAFETY EQUIP section.
4. Turn ignition off. Using DVOM, backprobe fuel level sensor input circuit at fuel level sensor connector. If reading is less than 0.13 volt, go to next step. If reading is greater than 0.13 volt, go to step 6).
5. Check for an open fuel level sensor input circuit. If an open is found, go to step 7). If an open does not exist, go to step 8).
6. Using DVOM connected to ground, backprobe fuel level sensor output terminal of fuel level sensor. If reading is greater than 2.9 volts, go to step 9). If reading is less than 2.9 volts, go to step 10).
7. Repair open in fuel level sensor input circuit. Go to step 11).
8. Repair open in fuel level sensor output circuit. Go to step 11).
9. Repair short to voltage in fuel level output circuit. Go to step 11).
10. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Go to next step.
11. Using scan tool, select DTC and clear DTC information. Start engine and idle to normal operating temperature. Select SPECIFIC DTC INFO for DTC set. Operate vehicle within the conditions for setting DTC P0462. If scan tool indicates diagnostic RAN AND PASSED, system is okay. If DTC does not indicate system RAN AND PASSED, go to step 2).

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Observe fuel level reading on scan tool. If reading displayed is 99-100%, go to step 4). If scan tool does not indicate specified amount, go to next step.
3. Test fuel gauge operation. See «INSTRUMENT PANEL»(ref-26406) article in ACCESSORIES/SAFETY EQUIP section.
4. Turn ignition off. Using DVOM, backprobe fuel level sensor input circuit at fuel level sensor connector. If reading is greater than 2.9 volts, go to next step. If reading is less than 2.9 volts, go to step 6).
5. Check for a short to voltage in fuel level input circuit. If a short to voltage is found, go to step 7). If a short to voltage does not exist, go to next step.
6. Check for open in fuel level output circuit. If a short to voltage is found, go to step 9). If a short to voltage does not exist, go to step 10).
7. Locate and repair short to voltage in fuel level sensor input circuit. Go to step 11).
8. Locate and repair short to voltage in fuel level sensor output circuit. Go to step 11).
9. Repair open in fuel level output circuit. Go to step 11).
10. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Go to next step.
11. Using scan tool, select DTC and clear DTC information. Start engine and idle to normal operating temperature. Select SPECIFIC DTC INFO for DTC set. Operate vehicle within the conditions for setting DTC P0463. If scan tool indicates diagnostic RAN AND PASSED, system is okay. If DTC does not indicate system RAN AND PASSED, go to step 2).

Scheme 14

PCM controls cooling low speed operation through the use of a low fan relay and a control circuit. If PCM commands fan low speed operation and senses fan did not turn on, or commands fan operation off and fan continues to run, DTC P0480 will be set.

Conditions required for setting DTC are

1. Ignition voltage is greater than 10 volts.
2. Engine run time is greater than 32 seconds.
3. PCM senses voltage is high with low speed fan off.
4. PCM senses voltage is low with low speed fan on.
5. Conditions are met for 25 seconds within a 50-second period.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Review and record scan tool failure records data, then clear DTCs. Operate vehicle within failure records that were recorded. Monitor specific DTC information for DTC P0480. If scan tool indicates DTC P0480 RAN and PASSED, check for poor connections, open circuit or shorted condition. If DTC P0480 is set, go to next step.
3. Turn ignition on. Remove low fan relay from underhood electrical center. Turn ignition on. Using DVOM, check for voltage at power feed terminal from ELEC. FAN (30-amp) fuse. If reading is about 12 volts, go to step 6). If reading is not about 12 volts, go to next step.
4. Using DVOM, check for voltage at power feed terminal of low speed relay connector from ENGINE FAN (15-amp) fuse. If reading is approximately 12 volts, go to step 6). If reading is not about 12 volts, go to next step.
5. Check low fan relay circuit and fuse for an open or shorted condition. Repair as necessary. Retest system.
6. Turn ignition off. Disconnect PCM connectors. Using a DVOM, check low fan circuits for an open or shorted condition. Repair as necessary. If circuits are okay, go to next step.
7. Install low fan relay. Using a fused jumper wire, ground low fan relay control circuit at appropriate PCM connector terminal. Turn ignition on. If fan runs at low speed, go to next step. If fan does not run at low speed, replace low fan relay.
8. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Review and record scan tool failure records data, then clear DTCs. Operate vehicle within failure records that were recorded. Monitor specific DTC information for DTC P0481. If scan tool indicates DTC P0481 RAN AND PASSED, check for poor connections, open circuit or shorted condition. If DTC P0481 is set, go to next step.
3. Turn ignition on. Remove high fan relay from underhood electrical center. Turn ignition on. Using DVOM, check for voltage at power feed terminal of high speed relay connector from ELEC. FAN (30-amp) fuse. If reading is about 12 volts, go to step 6). If reading is not about 12 volts, go to next step.
4. Using DVOM, check for voltage at power feed terminal of high speed relay connector from ENGINE FAN (15-amp) fuse. If reading is about 12 volts, go to step 6). If reading is not about 12 volts, go to next step.
5. Check high fan relay circuit and appropriate fuses for an open or shorted condition. Repair as necessary. Retest system.
6. Turn ignition off. Disconnect PCM connectors. Using a DVOM, check high fan circuits for an open or shorted condition. Repair as necessary. If circuits are okay, go to next step.
7. Install high fan relay. Using a fused jumper wire, ground high fan relay control circuit at appropriate PCM connector terminal. Turn ignition on. If fan runs at high speed, go to next step. If fan does not run at high speed, replace high fan relay.
8. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

Scheme 15

The VSS circuit uses a Hall Effect switch to inform the PCM of vehicle speed.

Conditions required to set DTC are

1. Engine is running.
2. ECT is above 140°F (60°C).
3. System voltage is 10-16 volts.
4. PCM detects no VSS signal.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition off. Disconnect VSS harness connector. Connect a test light to positive battery post. Probe VSS connector ground terminal. If test light illuminates, go to next step. If test light does not illuminate, repair ground circuit as necessary. Retest system.
3. With sensor disconnected, turn ignition on. Using DVOM, probe VSS connectors ground and voltage supply. If battery voltage is displayed, go to next step. If battery voltage is not displayed on DVOM, repair open or short to ground which may have blown meter fuse. Retest system.
4. Disconnect PCM connectors. Using a DVOM, check VSS input circuit between VSS connector and appropriate PCM harness connector. If resistance is greater than 10 ohms, system is okay at this time. If reading is less than 10 ohms, replace VSS sensor.

Scheme 16

PCM controls idle speed by adjusting an Idle Air Control (IAC) valve to a calculated RPM based on sensor inputs and actual engine RPM. PCM moves IAC pintle valve in or out to vary amount of air flowing into intake manifold, and thus decrease or increase idle RPM. PCM commands IAC in counts. A higher count allows more air to by-pass throttle plate (higher idle). When PCM detects too low of an idle speed and is unable to adjust idle speed, DTC P0506 will be set and MIL will be illuminate on second consecutive trip this is detected.

Conditions required to set DTC are

1. Engine run time is more than 125 seconds.
2. No ECT, EGR, IAT, MAP, TP or VSS sensor DTCs set.
3. No EVAP system, fuel trim or low voltage DTCs set.
4. BARO is greater than 72.7 kPa.
5. Canister purge duty cycle is above 0%.
6. ECT is greater than 120°F (50°C).
7. IAT is more than -40° (-40°C).
8. MAP is less than 60 kPa.
9. Throttle is closed.
10. Ignition voltage is 9.5-16.7 volts.
11. Engine speed is 100 RPM lower than desired idle.
12. Listed conditions are met for greater than 10 seconds.

Check for faulty connection at IAC and PCM connectors. Check for damaged harness. Check for restrictions, collapse or blockage in air intake system, air ducts or air filter. Check throttle body bore and IAC for excessive deposits. Check for large vacuum leak, such as incorrectly installed PCV valve or disconnected brake booster hose. Check for restricted air intake system. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using scan tool, read DTCs. If any other DTCs are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
3. Start engine. Turn all accessories off. Using scan tool, monitor ENGINE SPEED and command engine speed up to 1500 RPM, down to 500 RPM, and up to 1500 RPM. If ENGINE SPEED remains within 50 RPM of desired RPM for each command, see «DIAGNOSTIC AIDS»(ref-16367-S34462166962001010800000) . If ENGINE SPEED is not as specified, go to next step.
4. Disconnect IAC harness connector. Install IAC Node Light (J37027 or equivalent) in IAC harness connector. With engine running, monitor node lights while commanding engine speed up to 1500 RPM, down to 500 RPM, and back up to 1500 RPM. Both node lights should cycle Green and Red, but not OFF as RPM changes from 500-1500 RPM. If lights flash as specified, go to step 6). If lights do not flash as specified, go to next step.
5. Check IAC "A" high and IAC "A" low, and IAC "B" high and IAC "B" low circuits for open or shorted condition. If such a condition is found, repair as necessary. Retest system. If no problem is found in high or low circuits, go to step 10).
6. Ensure throttle stop screw has not been tampered with. Check for stuck IAC valve or throttle linkage. Check for restrictions, collapse or blockage in air intake system, air ducts or air filter. Check throttle body bore and IAC for excessive deposits. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
7. Check for faulty connection at IAC harness connector. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
8. Using a DVOM, check IAC valve solenoids for an open, short to ground or shorted together condition. If such condition exists, go to next step. If no problem is found with IAC valve solenoids, go to step 10).
9. Replace IAC valve. Retest system.
10. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform ON-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using scan tool, read DTCs. If any other DTCs are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
3. Start engine. Turn all accessories off. Using scan tool, monitor ENGINE SPEED and command engine speed up to 1500 RPM, down to 500 RPM, and back up to 1500 RPM. If ENGINE SPEED remains within 50 RPM of desired RPM for each command, go to «DIAGNOSTIC AIDS»(ref-16367-S14867768912001010800000) . If ENGINE SPEED is not as specified, to next step.
4. Disconnect IAC harness connector. Install IAC Node Light (J37027) in IAC harness connector. Monitor node lights while commanding engine speed up to 1500 RPM, down to 500 RPM, and up to 1500 RPM. Both node lights should cycle Green and Red, but not OFF as RPM changes from 500-1500 RPM. If lights flash as specified, go to step 6). If lights do not flash as specified, go to next step.
5. Check IAC "A" low and IAC "A" high, and IAC "B" low and IAC "B" high circuits for open or shorted condition. If such a condition is found, repair as necessary. Retest system. If no problem is found, go to step 10).
6. Check for vacuum leaks. Ensure throttle stop screw has not been tampered with. Check for throttle plate or shaft binding. Check accelerator and speed control cables for misadjustment or binding. Check for faulty, missing or incorrectly installed PCV valve. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
7. Check for faulty connection at IAC harness connector. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
8. Using a DVOM, check IAC valve solenoids for an open, short to ground or shorted together condition. If such condition exists, go to next step. If no problem is found with IAC valve solenoids, go to step 10).
9. Replace IAC valve. Retest system.
10. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

Scheme 17

PCM monitors A/C refrigerant pressure through the use of a 3-wire sensor. If PCM senses the pressure falls below a threshold value, then DTC P0532 will set.

Conditions required to set DTC are

1. A/C pressure sensor is below 5 counts (.1 volts) for 125 seconds for a period of 250 seconds.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Review and record FAILURE RECORDS data, then clear DTCs. Operate vehicle within data recorded. Check for DTC P0532. If DTC P0532 is present, go to next step. If DTC does not exist, check for poor connections and/or intermittent open or shorted condition.
3. Turn ignition off. Disconnect A/C refrigerant pressure sensor. Start vehicle and monitor A/C pressure value. If reading holds steady at less than .1 volt, go to step 5). If reading does not hold steady, go to next step.
4. Check A/C pressure sensor signal circuit between PCM and A/C pressure sensor for a short to voltage. If short to voltage is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Check A/C pressure sensor signal circuit between PCM and A/C pressure sensor for a short to ground or an open circuit. Repair as necessary. If circuit is okay, go to next step.
6. Check A/C pressure sensor 5-volt reference circuit between PCM and A/C pressure sensor for a shorted or open condition. Repair as necessary. If circuit is okay, go to next step.
7. Turn ignition off. Connect a DVOM between 5-volt reference terminal of A/C pressure sensor connector. Turn ignition on. If DVOM reading is about 5 volts, go to next step. If reading is not about 5 volts, go to step 12).
8. Turn ignition off. Using a fused jumper wire, connect A/C pressure sensor harness connector 5-volt reference and A/C pressure sensor signal terminals. Turn ignition on. Using scan tool, observe A/C pressure sensor value. If value is about 5 volts, go to next step. If value is not about 5 volts, go to step 12).
9. Using DVOM, measure resistance across A/C pressure sensor terminals. If an open condition is found, replace A/C pressure sensor. If no problem is found, go to next step.
10. Turn ignition off. Using DVOM, connect leads between A/C pressure sensor connector sensor ground and 5-volt reference terminals. Turn ignition on. If reading is about 5 volts, go to next step. If reading is not about 5 volts, go to step 12).
11. Replace A/C refrigerant pressure sensor. Retest system.
12. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on. Review and record FAILURE RECORDS data, then clear DTCs. Operate vehicle within data recorded. Check for DTC P0533. If DTC P0533 is present, go to next step. If DTC does not exist, check for poor connections and/or intermittent open or shorted condition.
3. Turn ignition off. Disconnect A/C refrigerant pressure sensor. Start vehicle and monitor A/C pressure value. If reading holds steady at less than .1 volt, go to step 5). If reading does not hold steady, go to next step.
4. Check A/C pressure sensor signal circuit between PCM and A/C pressure sensor for a short to voltage. If short to voltage is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Check A/C pressure sensor signal circuit between PCM and A/C pressure sensor for a short to ground or an open circuit. Repair as necessary. If circuit is okay, go to next step.
6. Check A/C pressure sensor 5-volt reference circuit between PCM and A/C pressure sensor for a shorted or open condition. Repair as necessary. If circuit is okay, go to next step.
7. Turn ignition off. Connect a DVOM between 5-volt reference terminal of A/C pressure sensor connector. Turn ignition on. If DVOM reading is about 5 volts, go to next step. If reading is not about 5 volts, go to step 12).
8. Turn ignition off. Using a fused jumper wire, connect A/C pressure sensor harness connector 5-volt reference and A/C pressure sensor signal terminals. Turn ignition on. Using scan tool, observe A/C pressure sensor value. If value is about 5 volts, go to next step. If value is not about 5 volts, go to step 12).
9. Using DVOM, measure resistance across A/C pressure sensor terminals. If an open condition is found, replace A/C pressure sensor. If no problem is found, go to next step.
10. Turn ignition off. Using DVOM, connect leads between A/C pressure sensor connector sensor ground and 5-volt reference terminals. Turn ignition on. If reading is about 5 volts, go to next step. If reading is not about 5 volts, go to step 12).
11. Replace A/C refrigerant pressure sensor. Retest system.
12. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

Scheme 18

PCM monitors the system voltage of the ignition feed terminals to the PCM. A system voltage DTC will set whenever the voltage is below a calibrated value.

Conditions required to set DTC are

1. Ignition is on.
2. System voltage is below 11.5 volts for 15 minutes.

If DTC sets when an accessory is operated, check for a poor connection or excessive current draw.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using DVOM, measure battery voltage at battery. If reading is greater than 11.5 volts, go to next step. If reading is 11.5 volts or less, charge battery before proceeding to next step.
3. Install scan tool and select IGNITION VOLTS. Place vehicle in Neutral or Park. Start engine, increase engine speed to 2000 RPM and load electrical system (turn on headlights, blower, radio, etc.). If scan tool reads about 13.2 volts, go to next step. If reading is not as specified, see appropriate «GENERATOR & REGULATOR»(ref-26407) article in ELECTRICAL section.
4. Turn ignition off. Disconnect PCM connector. Turn ignition on, engine off. Using a DVOM, measure ignition voltage at PCM. If output is equal to battery voltage, check for excessive current draw with ignition off. If voltage is not equal to battery voltage, go to next step.
5. Check for poor connections at PCM harness terminals. Repair as necessary. Retest system. If no problem is found, go to next step.
6. Check for an open ignition feed circuit to PCM. Repair as necessary. Retest system. If no problem is found, go to next step.
7. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

PCM monitors the system voltage of the ignition feed terminal to the PCM. A system voltage DTC will set whenever the voltage is above a calibrated value.

Conditions required to set DTC are

1. Ignition is on.
2. System voltage is above 16 volts for 15 minutes.

If DTC sets when an accessory is operated, check for a poor connection or excessive current draw.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using DVOM, measure battery voltage at battery. If reading is less than 11.5 volts, go to next step. If reading is 11.5 volts or more, go to step 4).
3. Charge battery and clean battery terminals and cable connections. If voltage is less than 11.5 volts, replace battery. If voltage is 11.5 volts or more, go next step.
4. Turn all accessories off. Install scan tool and select ignition voltage parameter. Place vehicle in Park or Neutral. Start engine and increase engine speed to 2000 RPM. If scan tool reading is more than 16 volts, replace or repair generator as necessary. See appropriate «GENERATOR & REGULATOR»(ref-26407) article in ELECTRICAL section. Retest system. If voltage is not as specified, go to next step.
5. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

PCM uses an Electrically Erasable Programmable Read Only Memory (EEPROM). EEPROM contains program information and calibrations required for engine, transaxle, and powertrain diagnostics operation.

Condition required to set DTC is

1. PCM detects an internal program fault (check sum error).

Only possible repair is replacement and programming of PCM.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. After repair is completed, retest system. Repeat On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using scan tool, select LAST TEST FAIL. Record any other failed DTCs. If DTC P0108 is also set, diagnose DTC P0108 before proceeding. If DTC is not set, go to next step.
3. If DTC P0463 and/or P1121 is also set, go to step 6). If none of these DTCs are set, go to next step.
4. Check for faulty sensor ground circuit terminal connection at MAP sensor. If problem is found, go to step 10). If no problem is found, go to next step.
5. Check MAP signal circuit between MAP sensor harness connector and PCM for intermittent short to voltage. If a problem is found, go to step 10). If no problem is found, go to step 8).
6. Check for intermittent short to voltage on 5-volt reference circuit between PCM and MAP, FTP and TP sensors. If a problem is found, go to step 10). If no problem is found, go to next step.
7. Check for faulty ground circuit terminal connection at PCM. If problem is found, go to step 9). If no problem is found, go to next step.
8. Check for intermittent open or faulty splice in sensor ground circuit. If a problem is found, go to step 10). If no problem is found, go to «DIAGNOSTIC AIDS»(ref-16367-S00944972732001010800000) .
9. Replace faulty connector terminal. Retest system.
10. Locate and repair intermittent open/short circuit. Retest system.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using scan tool, record any other failed DTCs. If DTC P0107 is also set, diagnose DTC P0107 before proceeding. If DTC is not set, go to next step.
3. If DTC P0462 and/or P1122 is also set, go to step 6). If DTC is not set, go to next step.
4. Check for faulty 5-volt reference or signal circuit connection at MAP sensor. If a problem is found, go to step 9). If no problem is found, go to next step.
5. Check signal circuit between MAP sensor and PCM for intermittent open or short to ground. If problem is found, go to step 10). If no problem is found, go to step 8).
6. Check for intermittent short to ground on 5-volt reference circuit between PCM and MAP, FTP and TP sensors. If a problem is found, go to step 10). If no problem is found, go to next step.
7. Check for faulty 5-volt reference circuit connection at PCM. If faulty connection is found, go to step 9). If connection is okay, go to next step.
8. Check for intermittent open or faulty splice in 5-volt reference circuit. If a problem is found, go to step 10). If no problem is found, go to «DIAGNOSTIC AIDS»(ref-16367-S13875006462001010800000) .
9. Replace faulty connector terminal(s). Retest system.
10. Repair circuit as necessary. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using scan tool, Record any other failed DTCs. If DTC P0113 is also set, diagnose DTC P0113 before proceeding. If DTC is not set, go to next step.
3. Check for a poor sensor ground circuit connection at IAT sensor connector. If problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
4. Check for poor IAT sensor signal circuit connection at IAT sensor connector. If problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Check IAT signal circuit between IAT sensor harness connector and PCM for intermittent open. If open is found, repair as necessary. Retest system. If no open is found, go to next step.
6. Check IAT signal circuit between IAT sensor harness connector and PCM for intermittent short to voltage. If short to voltage is found, repair as necessary. Retest system. If no short to voltage is found, go to next step.
7. Check for faulty ground circuit terminal connection at PCM. If problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
8. Check for intermittent open or faulty splice in sensor ground circuit. If a problem is found, repair as necessary. Retest system. If no problem is found, see «DIAGNOSTIC AIDS»(ref-16367-S33431822452001010800000) .

Diagnostic Procedures

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using scan tool, record any other failed DTCs. If DTC P0112 is also set, diagnose DTC P1111 before proceeding. If DTC is not set, go to next step.
3. Check IAT signal circuit between IAT sensor harness connector and PCM for intermittent short to ground. If short to ground is found, repair as necessary. Retest system. If no short to ground is found, see «DIAGNOSTIC AIDS»(ref-16367-S36002744502001010800000) .

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using scan tool, record any other failed DTCs. If DTC P0117 is also set, diagnose DTC P0117 before proceeding. If DTC is not set, go to next step.
3. Check ECT signal circuit between ECT sensor harness connector and PCM for intermittent short to ground. If short to ground is found, repair as necessary. Retest system. If no short to ground is found, see DIAGNOSTIC AIDS.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using scan tool, record any other failed DTCs. If DTC P0118 is also set, diagnose DTC P0118 before proceeding. If DTC is not set, go to next step.
3. If DTC P1106, P1111, and/or P1121 is also set, go to step 8). If none of these DTCs are set, go to next step.
4. Check for faulty sensor ground circuit terminal at ECT sensor. If problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
5. Check for faulty signal circuit connection at ECT sensor. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
6. Check ECT signal circuit between ECT sensor harness connector and PCM for intermittent open. If open is found, repair as necessary. Retest system. If no open is found, go to next step.
7. Check ECT signal circuit between ECT sensor harness connector and PCM for intermittent short to voltage. If short to voltage is found, repair as necessary. Retest system. If no short to voltage is found, go to next step.
8. Check for faulty ground circuit terminal connection at PCM. If problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
9. Check for intermittent open or faulty splice in sensor ground circuit. If a problem is found, repair as necessary. Retest system. If no problem is found, see «DIAGNOSTIC AIDS»(ref-16367-S32122838832001010800000) .

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using scan tool, record any other failed DTCs. If DTC P0123 is also set, diagnose DTC P0123 before proceeding. If DTC is not set, go to next step.
3. If DTC P0463 or P1106 is also set, go to step 6). If none of these DTCs are set, go to next step.
4. Check for faulty sensor ground circuit terminal at TP sensor. If problem is found, go to step 9). If no problem is found, go to next step.
5. Check TP signal circuit between TP sensor harness connector and PCM for intermittent short to voltage. If a problem is found, go to step 10). If no problem is found, go to step 8).
6. Check for intermittent short to voltage on 5-volt reference circuit between PCM and MAP or FTP sensor. If a problem is found, go to step 10). If no problem is found, go to next step.
7. Check for faulty ground circuit terminal connection at PCM. If problem is found, go to step 9). If no problem is found, go to next step.
8. Check for intermittent open or faulty splice in sensor ground circuit. If a problem is found, go to step 10). If no problem is found, see «DIAGNOSTIC AIDS»(ref-16367-S30120521042001010800000) .
9. Replace faulty connector terminal. Retest system.
10. Locate and repair intermittent open/short circuit. Retest system.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using scan tool, record any other failed DTCs. If DTC P0122 is also set, diagnose DTC P0122 before proceeding. If DTC is not set, go to next step.
3. If DTC P1107 and/or P0462 is also set, go to step 6). If DTCs are not set, go to next step.
4. Check for faulty 5-volt reference or signal circuit connection at TP sensor. If a problem is found, go to step 9). If no problem is found, go to next step.
5. Check signal circuit between TP sensor and PCM for intermittent open or short to ground. If problem is found, go to step 10). If no problem is found, go to step 8).
6. Check for intermittent short to ground on 5-volt reference circuit between PCM and MAP or FTP sensor. If a problem is found, go to step 10). If no problem is found, go to next step.
7. Check for faulty 5-volt reference circuit connection at PCM. If faulty connection is found, go to step 9). If connection is okay, go to next step.
8. Check for intermittent open or faulty splice in 5-volt reference circuit. If a problem is found, go to step 10). If no problem is found, see «DIAGNOSTIC AIDS»(ref-16367-S10658411962001010800000) .
9. Replace faulty connector terminal(s). Retest system.
10. Repair intermittent open/short circuit in wiring harness as necessary. Retest system.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using scan tool, record any other failed DTCs. If any DTC other than P1153 or P1154 sets, diagnose affected DTC before proceeding. If no other DTC sets, start engine and allow it to idle. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1133 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1133 FAILED THIS IGN, go to «DIAGNOSTIC AIDS»(ref-16367-S06454571302001010800000) .
3. Using scan tool, select LAST TEST FAIL. Record any other failed DTCs. If DTC P1153 or P1154 is also set, go to step 11). If DTC is not set, go to next step.
4. Check exhaust system for leaks. If exhaust leak is found, repair as necessary and go to step 2). If no exhaust leak is found, go to next step.
5. Visually inspect front HO2S for secure installation or corrosion on terminals. Check terminal tension at front HO2S and PCM. Check for damaged wiring. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
6. Disconnect front HO2S connector. Connect a DVOM to PCM side of connectors high signal and ground, and low signal and ground. Turn ignition on and read DVOM at each connection. If reading is 3-4 mV, go to step 9). If voltage is not as specified, go to next step.
7. Turn ignition off and check for damage to PCM pins or terminals. If a problem was found, repair as necessary and retest system. If no problem was found, go to next step.
8. Inspect signal circuit for a short to voltage, ground or an open. If problem was found, repair as necessary. Retest system. If no problem was found, go to next step.
9. With ignition off, disconnect PCM connector. Disconnect HO2S and check for high and low signal circuits, located between PCM and HO2S, for shorting together. If a problem was found, repair as necessary. Retest system. If no problem was found, go to next step.
10. Connect PCM and disconnected front HO2S. Using scan tool, check voltage. If reading is .43-.47 volts, go to step 12). If voltage is not as specified, go to step 13).
11. Check for fuel contamination, use of improper RTV sealant or excessive engine oil and coolant consumption. Replace affected HO2S. Retest system.
12. Replace front HO2S. Retest system.
13. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Using scan tool, select LAST TEST FAIL. Record any other failed DTCs. If any DTC other than P1153 or P1154 sets, diagnose affected DTC before proceeding. If no other DTC sets, start engine and allow it to idle. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1134 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1134 FAILED THIS IGN, go to «DIAGNOSTIC AIDS»(ref-16367-S14691996132001010800000) .
3. Check exhaust system for leaks. If exhaust leak is found, repair as necessary. Retest system. If no exhaust leak is found, go to next step.
4. Visually inspect front HO2S for secure installation or corrosion on terminals. Check terminal tension at front HO2S and PCM. Check for damaged wiring. If a problem is found, go to step 7). If no problem is found, go to next step.
5. Disconnect front HO2S connector. Turn ignition on. Using DVOM, measure voltage between high signal circuit and ground, and low signal circuit and ground. If DVOM reads 3-4 volts, go to next step. If voltage is not as specified, go to step 8).
6. Turn ignition off. With front HO2S disconnected, connect a jumper wire between front HO2S harness connector high signal circuit, low signal circuit and ground. Turn ignition on. If scan tool reading jumps from .01 volt to .45 volt when jumper is removed, go to step 10). If voltage does not change as specified, go to step 11).
7. Repair condition as necessary. Retest system.
8. Check for poor PCM connections or terminal damage. Repair as necessary. Retest system. If no problem is found, go to next step.
9. Repair open, grounded or shorted signal circuit. Retest system. If no problem is found, go to step 6).
10. Remove front HO2S. Check for fuel contamination, improper RTV sealant (White powdery coating on sensor), and excessive engine oil or coolant consumption. Repair as necessary and go to step 13). If no problem is found, go to step 12).
11. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.
12. Replace front HO2S. Retest system.
13. Before replacing front HO2S, correct cause of contamination. Retest system.

Scheme 19

When power enrichment is requested from PCM, the PCM monitors HO2S reading to ensure power enrichment (heavy acceleration) has been achieved. If during power enrichment, rich exhaust is not detected by the PCM, DTC 1171 will set.

Conditions required to set DTC are

1. No related DTCs are set.
2. Engine is operating in closed loop power enrichment mode.
3. ECT is above 140°F (60°C).
4. HO2S voltage remains below .4 volt for 5 seconds while in power enrichment mode.

A restricted fuel filter or fuel line can supply adequate amounts of fuel at idle, but may not be able to supply enough fuel during heavy acceleration. Water or alcohol in the fuel may cause low HO2S voltage during acceleration. Check for faulty or plugged fuel injectors or low fuel level.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. If any other component-related DTCs are set, fix those DTCs first. If no other DTC is present, go to next step.
3. Check fuel level. Add fuel if tank is almost empty. If fuel was added, go to next step. If no additional fuel was required, go to step 5).
4. Start vehicle and bring engine to normal operating temperature of 167-203°F (75-95°C). Increase engine speed to 1200 RPM and, using scan tool, observe HO2S-1 voltage. If scan tool reading toggles between .1 and .9 volt, see FUEL SYSTEM DIAGNOSIS under appropriate TROUBLE SHOOTING in «BASIC TESTING»(ref-16362) article. If voltage is not as specified, go to next step.
5. Turn ignition off. Disconnect fuel pump relay. Crank engine to relieve fuel pressure. Install fuel pressure gauge. Reinstall fuel pump relay. Start engine, bring to normal operating temperature and allow it to idle. Disconnect vacuum line going to fuel pressure regulator and read pressure gauge. If pressure is 41-47 psi (2.9-3.3 kg/cm 2 ), see On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. If pressure reading is not as specified, go to next step.
6. Check for restricted fuel lines or filter. If problem is found, repair problem. Retest system. If no problem is found, go to next step.
7. Turn ignition on, engine off. Using scan tool, turn on fuel pump. With fuel pressure gauge still connected, pinch off fuel return line, not allowing fuel pressure to exceed 60 psi (4.2 kg/cm 2 ). Manipulate fuel line to raise pressure above 47 psi (3.3 kg/cm 2 ). If pressure rises above specification, go to «DIAGNOSTIC AIDS»(ref-16367-S36589673082001010800000) . If pressure does not rise above specification, go to next step.
8. Check for faulty fuel pump, restricted fuel pump strainer, incorrect fuel pump, incorrect fuel being used or hot fuel. If any problem is found, repair as necessary. Retest system.

Crankshaft position system variation learning feature is used to calculate reference period errors caused by slight tolerance variations in crankshaft, crankshaft balancer interrupter rings, and Crankshaft Position (CKP) sensor Hall Effect switches. The calculated error allows PCM to accurately compensate for reference period variations. The crankshaft position system variation learning feature enhances the ability of the PCM to detect misfire events over a wider range of engine speed and load.

Note. The crankshaft position system variation learning procedure must be performed anytime a change is made to the CKP sensor to crankshaft relationship, or if PCM is replaced or reprogrammed.

DTC P1336 indicates that the crankshaft position system variation values have not been stored in the PCM and the crankshaft position system variation learn procedure must be performed. The learning procedure is required after the following service procedures have been performed, regardless of whether or not DTC P1336 is set

1. PCM replacement.
2. Engine replacement.
3. Crankshaft balancer replacement.
4. Crankshaft position sensor replacement.
5. Any engine repair(s) which disturbs crankshaft/harmonic balancer to crankshaft position sensor relationship.

Conditions required for setting DTC

1. Crankshaft position system variation values are not stored in the PCM memory.
2. PCM has not successfully learned crankshaft position Tooth Error Correction (TEC) within 5 attempts or 3 miles.

DTC P1336 will only set if PCM has not learned the crankshaft position system variation. PCM only needs to learn this variation once per life cycle of vehicle unless the CKP sensor to crankshaft relationship is disturbed. Removing a part for inspection and then reinstalling the same part is considered a disturbance. A fully warmed up engine is critical to learning the variation correctly. If a valid learn occurs, no other learns can be completed that ignition cycle.

If engine cuts out before the specified learn procedure engine speed or at normal fuel cut-off RPM, the PCM is not in the learn procedure mode. Review crankshaft position system variation learning procedure and re-enable the learn procedure. Verify that scan tool indicates TEST IN PROGRESS.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. After performing OBD-II system check, go to next step.
2. Perform crankshaft position system variation learn position as follows: Install scan tool. Transaxle is in Park or Neutral. ECT at 185°F (85°C). Engage parking brake. Block vehicle drive wheels. All accessories off, start vehicle and warm to normal operating temperature. Enable crankshaft position system variation learning procedure with scan tool. Increase engine speed to 3920 RPM and release throttle as soon as engine cuts out. If scan tool indicates that crankshaft position system variation has been learned, go to step 5). If scan tool does not indicate as specified, go to next step.
3. Attempt crankshaft position system variation learning procedures about 5 times. If crankshaft variation has not been learned, go to next step. If crankshaft variation has been learned, go to step 5).
4. Check for problem with crank sensor to crankshaft relationship. Repair as necessary. After repairs, go to next step.
5. Using scan tool, select DTC, then CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, then SPECIFIC, then enter DTC P1336. Operate vehicle within the conditions for setting this DTC. If scan tool indicates test RAN AND PASSED, go to next step. If scan tool does not indicate test RAN AND PASSED, repeat step 2).
6. Using scan tool, select CAPTURE INFO, then REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. After performing OBD-II system check, go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, check for ABS DTCs. If any ABS DTCs are set, go to next step. If no ABS DTCs are set, go to step 4).
3. Repair ABS system as necessary. See «ANTI-LOCK BRAKE SYSTEM»(ref-26408) article in BRAKES section. After repair, go to next step.
4. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. If misfire DTC is set, go to next step. If misfire DTC did not set, go to step 9).
5. If DTC P1381 also set, go to next step. If DTC P1381 did not set, go to step 7).
6. If ABS DTC is also set, go to step 3). If ABS DTC is not set, go to step 8).
7. Repair condition causing misfire as necessary. After repair, go to step 9).
8. Replace PCM. Program replacement PCM using appropriate equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. After repair is completed, go to next step.
9. Using scan tool, select CLEAR INFO or CLEAR DTCS function to clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function, then enter DTC P1380. If scan tool indicates test RAN AND PASSED, go to next step. If scan tool does not indicate test RAN AND PASSED, repeat step 2).
10. If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, no problem is indicated at this time.

1. Perform On-Board Diagnostic II (OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. After performing OBD-II system check, go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, attempt to display ABS data. If ABS data can be displayed, go to next step. If ABS data cannot be displayed, go to step 4).
3. Using scan tool, select CLEAR INFO or CLEAR DTCS function to clear DTCs. Review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. If a misfire DTC set, go to step 5). If a misfire DTC did not set, go to step 9).
4. Repair condition causing ABS data not to be displayed. See appropriate ANTI-LOCK BRAKES article in BRAKES section. After repairs, go to step 3).
5. If DTC P1380 also set, go to next step. If DTC P1380 did not set, go to step 7).
6. If ABS data can be displayed, go to step 8). If ABS data cannot be displayed, go to step 4).
7. Repair condition causing misfire as necessary. After repair is completed, go to step 9).
8. Replace PCM. Program replacement PCM using appropriate equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. After replacing PCM, go to next step.
9. Using scan tool, select CLEAR INFO or CLEAR DTCS function to clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function then enter DTC P1381. If scan tool indicates test RAN AND PASSED, go to next step. If scan tool does not indicate test RAN AND PASSED, repeat step 2).
10. If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, no problem is indicated at this time.

1. Perform On-Board Diagnostic II(OBD-II) system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on, with engine off. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within FAILURE RECORDS as noted on scan tool. Operate vehicle within FAILURE RECORDS data as recorded. If scan tool displays DTC P1404 RAN AND PASSED, go to «DIAGNOSTIC AIDS»(ref-16367-S20090352422001010800000) . If scan tool does not display DTC P1404 RAN AND PASSED, go to next step.
3. Turn ignition off. Disconnect EGR valve electrical connector. Turn ignition on. Using a DVOM, check for voltage at ignition feed circuit at EGR harness connector. If 12 volts exists, go to step 5). If 12 volts does not exist, go to next step.
4. Check ignition feed circuit between ENGINE IG (15-amp) fuse in instrument panel fuse block to EGR harness connector. Repair as necessary. Retest system. If circuit is okay, go to step 7).
5. Check resistance of EGR solenoid. If reading is less then 5 ohms, go to next step. If reading is greater than 5 ohms, go to step 14).
6. Check EGR LOW circuit between EGR sensor and PCM for an open or shorted condition. If such a condition should exist, repair as necessary and retest system. If such condition does not exist, go to step 15).
7. Turn ignition off. Disconnect EGR valve electrical connector. Turn ignition on. Using scan tool, observe EGR value. If reading is 0 VOLTS 9). If reading is not as specified, go to next step.
8. Check EGR feedback circuit between PCM and EGR valve sensor for an open or shorted condition. If such condition is found, repair as necessary and retest system. If such condition does not exist, go to step 15).
9. Turn ignition on. Using a DVOM, check for voltage at 5-volt reference signal terminal of EGR harness connector. If reading is about 5 volts, go to step 11). If reading is not about 5 volts, go to next step.
10. Check EGR 5-volt reference circuit between PCM and EGR valve sensor for an open or shorted condition. If such condition is found, repair as necessary and retest system. If such condition does not exist, go to next step.
11. Turn ignition off. Connect DVOM leads between 5-volt reference and signal return terminals of EGR valve harness connector. Turn ignition on. If reading is about 5 volts, go to step 13). If reading is not about 5 volts, go to next step.
12. Check signal return circuit between PCM and EGR valve sensor for an open or shorted condition. If such condition is found, repair as necessary and retest system. If such condition does not exist, go to step 15).
13. Turn ignition off. Connect a fused jumper wire between 5-volt reference circuit and EGR position feedback signal circuit terminals of EGR harness connector. Observe EGR value on scan tool. If reading indicates 5 VOLTS - 100%, go to next step. If reading is not as specified, go to step 15).
14. Replace EGR valve. Retest system.
15. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system.

1. Perform On-Board Diagnostic IIOBD-II system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Turn ignition on, engine off. Remove gas cap. Using scan tool, read FUEL TANK VACUUM. If scan tool displays 0 IN. H2O, go to next step. If scan does not display 0 IN. H2O, go to «DIAGNOSTIC AIDS»(ref-16367-S13554428382001010800000) .
3. Replace gas cap. Review and record FREEZE FRAME data for DTC P1441 and clear DTC information. Connect EVAP Diagnostic Station (P/N J41413), or similar, to EVAP service port. Using scan tool, command EVAP vent solenoid ON (closed). Attempt to pressurize EVAP system. If 5 in. H2O can be achieved, go to next step. If 5 in. H2O cannot be achieved, go to step 5).
4. Maintain tank pressure at 5 inches of H2O. Observe FUEL TANK VACUUM on scan tool. If fuel tank vacuum is at -5 in. H2O, go to step 6). If fuel tank vacuum cannot be held at -5 in. H2O, go to step 7).
5. Remove engine vacuum supply line from EVAP purge solenoid fitting. Install a hand held vacuum pump to fitting and apply 15 in Hg. If solenoid maintains vacuum, go to next step. If vacuum cannot be maintained, go to step 7).
6. Ensure vacuum supply line is routed properly and does not have any leaks. If no leaks are found, and hoses are properly routed, go to «DIAGNOSTIC AIDS»(ref-16367-S13554428382001010800000) . If improper routing or a leak is detected, go to step 8).
7. Replace EVAP purge solenoid. Go to step 9).
8. Correct improper routing or leakage in EVAP purge line as necessary. Go to next step.
9. Start engine. Remove fuel filler cap. Using scan tool, command EVAP vent solenoid ON (closed) and EVAP purge solenoid OFF (0%). Replace fuel filler cap. Run engine at 2500 RPM while monitoring FUEL TANK VACUUM on scan tool. If reading remains at 0 IN. H2O, repair is complete. If reading does not maintain as specified, go to step 1).

1. Perform On-Board Diagnostic IIOBD-II system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Ignition ON, Engine OFF. Review and record Scan Tool Failure Records data, then clear the DTCs. Operate the vehicle within the Failure Records conditions as noted. Using the Scan Tool, monitor "Specific DTC" info. for DTC P1546. Does the Scan Tool indicate DTC P1546 "Ran and Passed"? If yes, refer to «Diagnostic Aids»(ref-16367-S31740846562002090400000) . If no, Go to next step.
3. Ignition OFF. Remove the A/C Compressor Clutch Relay from the Underhood Electrical Center. Ignition ON, Engine OFF. Using a Digital Voltmeter (DVM), check for voltage on the fused pins of the A/C Compressor Clutch Relay connector. If DVM is showing 12 volts, go to Step 5 . If 12 volts is not shown, go to Step 4 .
4. Check the suspect circuit(s) between the A/C Compressor Clutch Relay connector and the fuse for the following conditions: A short to ground, an open circuit or a short to voltage. Repair as necessary. Verify Repair.
5. Ignition OFF. Disconnect the Powertrain Control Module (PCM) connectors from the PCM. Check the A/C Compressor Clutch Relay control circuit between the PCM and Underhood Electrical Center for the following conditions: A short to ground, an open circuit or a short to voltage. If problem was found, repair as necessary. Verify Repair. If problem was not found, go to next step.
6. Reinstall the A/C Compressor Clutch Relay. Using a fused jumper, ground the A/C Compressor Clutch Relay control circuit at the PCM connector. Ignition ON, Engine OFF. If the A/C Compressor turns ON, go to Step 9 . If compressor does not turn ON, go to Step Go to next step.
7. Ignition OFF. Check the A/C Compressor Clutch circuit between the A/C Compressor Clutch Relay and A/C Compressor Clutch for the following conditions: A short to ground, an open circuit or a short to voltage. If problem was found, repair as necessary. Verify Repair. If problem was not found, go to next step.
8. Replace the A/C Compressor Clutch Relay. Verify Repair.
9. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system, verify repair.

Scheme 20

The Powertrain Control Module (PCM) monitors the 5 volt reference signal when the Ignition is ON. If the PCM senses an Analog to Digital (A/D) conversion error within the PCM, then DTC P1627 will set. DTC P1627 is a type A code.

Conditions required for setting this DTC are

1. Engine is running.
2. Any A/D DTC's set.

Check for poor connections, or a damaged harness, inspect the harness connectors for: backed-out terminals, improper mating or damaged terminals. Also, check for open circuits, shorts to ground, and shorts to voltage.

1. Perform On-Board Diagnostic IIOBD-II system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Ignition ON, engine OFF. Review and record Scan Tool Failure Records data, then clear the DTCs. Operate the vehicle within the Failure Records conditions as noted. Using the Scan Tool, monitor "Specific DTC" info. for DTC P1627. Does the Scan Tool indicate DTC P1627 "Ran and PASSED"? If yes, refer to «Diagnostic Aids»(ref-16367-S07617339772002090500000) . If no, go to next step.
3. Check the suspect 5 volt reference circuit(s) for the following conditions: A short to ground, an open circuit and a short to voltage. If problem was found, repair as necessary. Verify Repair. If problem was not found, go to next step.
4. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system, verify repair.

1. Perform On-Board Diagnostic IIOBD-II system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Ignition ON, engine OFF. Review and record Scan Tool Failure Records data, then clear the DTCs. Operate the vehicle within the Failure Records conditions as noted. Using the Scan Tool, monitor "Specific DTC" info. for DTC P1635. Does the Scan Tool indicate DTC P1635 "Ran and PASSED"? If yes, refer to «Diagnostic Aids»(ref-16367-S07617339772002090500000) . If no, go to next step.
3. Check the suspect 5 volt reference circuit(s) for the following conditions: A short to ground, an open circuit and a short to voltage. If problem was found, repair as necessary. Verify Repair. If problem was not found, go to next step.
4. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system, verify repair.

Scheme 21

Output driver modules (ODMs) are used by the powertrain control module (PCM) to turn ON many of the current-driven devices that are needed to control various engine and transmission functions. Each ODM is capable of controlling up to 7 separate outputs by applying ground to the device which the PCM is commanding ON. ODMs have the capability of diagnosing each output circuit individually. DTC P1640 set indicates an improper voltage level has been detected on an ODM output.

If the PCM detects an open circuit condition and a shorted to voltage circuit condition on the same circuit at the same time, then DTC P1640 will set. DTC P1640 is a type D code.

Conditions required for setting this DTC are

1. Ignition switch on.
2. Conditions occur for at least 2.5 seconds.
3. The PCM detects an open circuit condition and a short to voltage circuit condition on the same circuit at the same time.

Poor connection at PCM - Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal-to-wire connection. Damaged harness - Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the PCM, turn the ignition ON and observe a voltmeter connected to the MIL driver circuit at the PCM harness connector while moving connectors and wiring harnesses relates to the MIL. A change in voltage will indicate the location of the fault. Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

1. Perform On-Board Diagnostic IIOBD-II system check. See «TESTS W/CODES - INTRODUCTION»(ref-16364) article. Go to next step.
2. Replace PCM. Program replacement PCM using required equipment. See «COMPUTER RELEARN PROCEDURES»(ref-12612) article in GENERAL INFORMATION section. Retest system, verify repair.