DTC P0601 - PCM MEMORY ERROR Isuzu Trooper II

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Replace PCM. After repair is completed, repeat OBD system check.

Diagnostic Aids

Inspect MAP sensor line for leakage or being plugged. Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. 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 P1111, P1115, 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 at MAP sensor. If problem is found, go to step 9). 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, EGR, "G" 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, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S22764003752001010800000) .
9. Replace faulty connector terminal. Retest system.
10. Locate and repair intermittent open/short circuit. Retest system.

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Using scan tool, select LAST TEST FAIL. 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 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 EGR valve, MAP, "G" 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, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S40786396222001010800000) .
9. Replace faulty connector terminal(s). Retest system.
10. Repair circuit as necessary. Retest system.

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Using scan tool, select LAST TEST FAIL. 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. If DTC P1106, P1115, 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 at IAT 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 IAT sensor. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
6. 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.
7. 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.
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, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S17347411362001010800000) .

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P0112 is also set, diagnose DTC P0112 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, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S36646716952001010800000) .

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. 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, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S29335524462001010800000) .

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. 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, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S08560635332001010800000) .

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P0123 is also set, diagnose DTC P0123 before proceeding. If DTC is not set, go to next step.
3. If DTC P1106, P1111, and/or P1115 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 tostep 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, EGR 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, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S12028786842001010800000) .
9. Replace faulty connector terminal. Retest system.
10. Locate and repair intermittent open/short circuit. Retest system.

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P0122 is also set, diagnose DTC P0122 before proceeding. If DTC is not set, go to next step.
3. If DTC P1107 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 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 EGR valve, MAP 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, check for an intermittent problem, see DIAGNOSTIC AIDS.
9. Replace faulty connector terminal(s). Retest system.
10. Repair circuit as necessary. Retest system.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation of HO2S heater circuit. If connections and wiring are okay and DTC continues to reset, replace HO2S 1. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. 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, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S32050566492001010800000) .
3. 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 HO2S No. 1 for secure installation or corrosion on terminals. Check terminal tension at HO2S No. 1 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 HO2S No. 1 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 millivolts, 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. 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 No. 1 and check for high and low signal circuits, located between PCM and HO2S No. 1 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 Bank 1 HO2S No. 1. Using scan tool, check voltage. If reading is 425-475 millivolts, go to step 12), If voltage is not as specified, got step 13).
11. Check for fuel contamination, use of improper RTV sealant or engine oil and coolant consumption. Replace affected HO2S. Retest system.
12. Replace HO2S 1. Retest system.
13. Replace PCM. Retest system.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation of HO2S heater circuit. If connections and wiring are okay and DTC continues to reset, replace HO2S 1. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. 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, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S34181812402001010800000) .
3. If DTC P1153 and/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. Retest system. If no exhaust leak is found, go to next step.
5. Visually inspect HO2S No. 1 for secure installation or corrosion on terminals. Check terminal tension at HO2S No. 1 and PCM. Check for damaged wiring. If a problem is found, go to step 8). If no problem is found, go to next step.
6. Disconnect HO2S No. 1 connector. Turn ignition on. Using DVOM, probe connector, 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 9).
7. Turn ignition off. With HO2S No. 1 disconnected, connect a jumper wire between HO2S No. 1 harness connector high signal, low signal circuits and ground. Turn ignition on. If scan tool reading jump from .01 volt to .45 volt when jumper is removed, go to step 11). If voltage does not change as specified, go to step 12).
8. Repair condition as necessary. Retest system.
9. Check for poor PCM connections or terminal damage. Repair as necessary. Retest system. If no problem is found, go to next step.
10. Repair open, grounded or shorted signal circuit. Retest system. If no problem is found, go to step 7).
11. Remove Bank 1 HO2S No. 1 and check it for fuel contamination, improper RTV sealant (white powdery coating on sensor) and engine oil or coolant consumption. Repair as necessary. Retest system. If no problem is found, go to step 13).
12. Replace PCM. Retest system.
13. Replace HO2S No. 1. Retest system.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation of HO2S heater circuit. If connections and wiring are okay and DTC continues to reset, replace HO2S 1. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any DTC other than P1133 or P1134 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 P1153 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1153 FAILED THIS IGN, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S14492153392001010800000) .
3. If DTC P1133 or P1134 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 HO2S No. 1 for secure installation or corrosion on terminals. Check terminal tension at HO2S No. 1 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 HO2S No. 1 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 millivolts, 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. 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 No. 1 and check for high and low signal circuits, located between PCM and HO2S No. 1 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 Bank 2 HO2S No. 1. Using scan tool, check voltage. If reading is 425-475 millivolts, go to step 12), If voltage is not as specified, got step 13).
11. Check for fuel contamination, use of improper RTV sealant or engine oil and coolant consumption. Replace affected HO2S. Retest system.
12. Replace HO2S 1. Retest system.
13. Replace PCM. Retest system.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation of HO2S heater circuit. If connections and wiring are okay and DTC continues to reset, replace HO2S 1. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any DTC other than P1133 or P1134 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 P1154 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1154 FAILED THIS IGN, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S05844018182001010800000) .
3. If DTC P1133 and/or P1134 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. Retest system. If no exhaust leak is found, go to next step.
5. Visually inspect HO2S No. 1 for secure installation or corrosion on terminals. Check terminal tension at HO2S No. 1 and PCM. Check for damaged wiring. If a problem is found, go to step 8). If no problem is found, go to next step.
6. Disconnect HO2S No. 1 connector. Turn ignition on. Using DVOM, probe connector, 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 9).
7. Turn ignition off. With HO2S No. 1 disconnected, connect a jumper wire between HO2S No. 1 harness connector high signal, low signal circuits and ground. Turn ignition on. If scan tool reading jump from .01 volt to .45 volt when jumper is removed, go to step 11). If voltage does not change as specified, go to step 12).
8. Repair condition as necessary. Retest system.
9. Check for poor PCM connections or terminal damage. Repair as necessary. Retest system. If no problem is found, go to next step.
10. Repair open, grounded or shorted signal circuit. Retest system. If no problem is found, go to step 7).
11. Remove Bank 2 HO2S No. 1 and check it for fuel contamination, improper RTV sealant (white powdery coating on sensor) and engine oil or coolant consumption. Repair as necessary. Retest system. If no problem is found, go to step 13).
12. Replace PCM. Retest system.
13. Replace HO2S No. 1. Retest system.

A restricted fuel system may provide adequate fuel supply at idle, but not during acceleration. Water or alcohol in fuel may cause low HO2S voltage during acceleration. Check for defective or plugged fuel injectors. Check for low fuel.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If any other component-related DTCs are set, diagnose them 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, 167-203°F (75-95°C). Raise engine speed to 1200 RPM and using scan tool observe HO2S No. 1 voltage. If scan tool reading toggle between .1 and .9 volt and voltage raise to high end of specification when throttle is opened half way for a few seconds, see INJECTOR BALANCE TEST in «SYSTEM/COMPONENT TESTS»(ref-16280) article. If voltage is not as specified, go to next step.
5. Turn ignition off. Relieve fuel pressure and install fuel pressure gauge. Start engine, bring to normal operating temperature and allow it to idle. Disconnect vacuum line to fuel pressure regulator and read pressure gauge. If pressure is 41-47 psi (280-325 kPa), see OBD II SYSTEM CHECK in «BASIC TESTING»(ref-16258) 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 as necessary. Retest system. If no problem is found, go to next step.
7. Turn ignition off. Remove fuel pump relay. Using a fused jumper between battery terminal and fuel pump fuse terminals. With fuel pressure gauge still connected, pinch off fuel return line, not allowing fuel pressure to exceed 60 psi (412 kPa). Manipulate fuel line to raise pressure greater than 47 psi (325 kPa). If pressure rises greater than 47 psi (325 kPa), check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S30644851322001010800000) . If pressure does not rise to 47 psi (325 kPa), go to next step.
8. Check for faulty fuel pump, restricted fuel pump strainer, incorrect fuel pump, incorrect fuel grade or hot fuel. If any problem is found, repair as necessary. Retest system.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If connections and wiring appear okay, monitor scan tool "G" sensor display while moving sensor connections and related harnesses. Change in scan tool display will indicate area of fault. MAP and "G" sensor share 5 volt reference and ground terminals. Defective MAP sensor or harness can set "G" sensor DTC. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P1392 is set, diagnose it first before proceeding. If no other DTC is set, go to next step.
3. Check for a poor connection at "G" sensor harness connector. If a problem is found, go to step 8). If no problem is found, go to next step.
4. Ensure ignition is off. Disconnect harness connectors from PCM and "G" sensor. Using DVOM, check "G" sensor signal circuit for an intermittent open or short to ground. If a problem was found, go to step 9). If no problem is found, go to next step.
5. Check reference circuit between PCM, MAP or "G" sensor for an intermittent short to ground. If a problem is found, go to step 9). If no problem is found, go to next step.
6. Check for poor 5-volt reference circuit terminal connection at PCM. If a problem is found, go to step 8). If no problem is found, go to next step.
7. Check for an intermittent open or a faulty splice in 5-volt reference circuit. If a problem is found, go to step 9). If no problem is found, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S02789225632001010800000) .
8. Repair 5-volt reference circuit and "G" sensor signal circuit harness connector terminals as necessary. Retest system.
9. Repair intermittent open or short circuit in wiring harness as necessary. Retest system.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If connections and wiring appear okay, monitor scan tool "G" sensor display while moving sensor connections and related harnesses. Change in scan tool display will indicate area of fault. MAP and "G" sensor share 5 volt reference and ground terminals. Defective MAP sensor or harness can set "G" sensor DTC. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Turn ignition on. Using scan tool, read and record FAIL RECORDS data for DTC P1391. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1391 FAILED THIS IGN, go to step 4). If scan tool does not display DTC P1391 FAILED THIS IGN, go to next step.
3. Check for "G" sensor seal missing, damaged or mounting flanges cracked, missing or incorrectly installed. If problem is found, repair as necessary. Retest system. If no problem is found, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S16790332662001010800000) .
4. Disconnect "G" sensor electrical connector. Using scan tool, observe "G" sensor value. If value is about zero volts, go to next step. If value is not as specified, go to step 12).
5. Connect jumper wire between "G" sensor reference and signal circuit at harness connector. Using scan tool, read "G" sensor value. If "G" sensor value is about 4.95 volts, go to next step. If value is not as specified, go to step 7).
6. Turn ignition off. Disconnect PCM connector. Check sensor ground circuit for high resistance, poor connection at PCM or an open between PCM and "G" sensor. If no problem is found, go to step 10). If a problem is found, repair as necessary. Retest system.
7. Check 5-volt reference circuit for high resistance, open between PCM and "G" sensor or a poor connection at PCM. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
8. Check signal circuit for high resistance, open, short to ground or short to sensor ground. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
9. Check "G" sensor circuit for poor connection at PCM. If a problem is found, repair as necessary. Retest system. If no problem is found, go to step 13).
10. Check for poor connection at "G" sensor. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
11. Replace "G" sensor. Retest system.
12. With ignition off, disconnect PCM. Turn ignition on. Check "G" sensor signal circuit for a short to voltage or short to 5-volt reference circuit. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
13. Replace PCM. Retest system.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If connections and wiring appear okay, monitor scan tool "G" sensor display while moving sensor connections and related harnesses. Change in scan tool display will indicate area of fault. MAP and "G" sensor share 5 volt reference and ground terminals. Defective MAP sensor or harness can set "G" sensor DTC. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Turn ignition on, engine off. Disconnect "G" sensor electrical connector. Using scan tool, observe "G" sensor value. If value is about zero volts, go to step 4). If value is not as specified, see ENGINE CRANKS BUT WILL NOT RUN in «BASIC TESTING»(ref-16258) article.
3. Turn ignition on. Using scan tool, read and record FAIL RECORDS data for DTC P1392. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1392 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1392 FAILED THIS IGN, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S41906361932001010800000) .
4. Disconnect "G" sensor electrical connector. Connect jumper wire between "G" sensor 5-volt reference and signal circuit at harness connector. Using scan tool, read "G" sensor value. If "G" sensor value is about 4.95 volts, go to step 9). If value is not as specified, go to next step.
5. Turn ignition off. Disconnect PCM and check 5-volt reference circuit for an open or short to ground. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
6. Check 5-volt reference circuit for a poor connection at PCM. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
7. With ignition off, disconnect PCM. Check "G" sensor signal circuit for open, short to ground or short to sensor ground. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
8. Check "G" sensor signal circuit for a poor connection at PCM. Repair as necessary. Retest system. If no problem is found, go to next step.
9. Replace PCM. Retest system.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If connections and wiring appear okay, monitor scan tool "G" sensor display while moving sensor connections and related harnesses. Change in scan tool display will indicate area of fault. MAP and "G" sensor share 5 volt reference and ground terminals. Defective MAP sensor or harness can set "G" sensor DTC. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Start engine and allow it to idle. Using scan tool read "G" sensor value. If value is greater than 4.5 volts (+3G), go to step 4). If value is 4.5 volts or less, go to next step.
3. Turn ignition on. Using scan tool, read and record FAIL RECORDS data for DTC P1393. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P1393 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1393 FAILED THIS IGN, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S23737175842001010800000) .
4. Turn ignition on, engine off. Disconnect "G" sensor electrical connector. Using scan tool, observe "G" sensor value. If value is not as specified, go to step 6). If value is about zero volts (-1G), go to next step.
5. Connect a test light to battery positive terminal and probe sensor ground. If test light illuminates, go to step 7). If test light does not illuminate, go to step 9).
6. With ignition off, disconnect PCM. Turn ignition on, engine off. Check "G" sensor signal circuit for a short to voltage or short to 5-volt reference circuit. If a problem is found, repair as necessary. Retest system. If no problem is found, go to step 11).
7. Check for poor sensor ground terminal connection at "G" sensor electrical connector. If a problem is found, replace faulty terminal. Retest system. If no problem is found, go to next step.
8. Check for a poor sensor ground terminal connection at PCM. If a problem is found, replace faulty terminal. Retest system. If problem is not found, go to next step.
9. Using DVOM, check continuity of "G" sensor ground circuit. If resistance is greater than 5 ohms, repair open or poor connection. Retest system. If no problem is found, go to next step.
10. Replace PCM. Retest system.
11. Replace "G" sensor. Retest system.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If connections and wiring appear okay, monitor scan tool "G" sensor display while moving sensor connections and related harnesses. Change in scan tool display will indicate area of fault. MAP and "G" sensor share 5 volt reference and ground terminals. Defective MAP sensor or harness can set "G" sensor DTC. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. If DTC P1393 is also set, repair P1393 first. If DTC P1393 is not set, go to next step.
3. If DTC P1106 and/or P1121 are also set, go to step 6). If DTC P1106 and/or P1121 are not set, go to next step.
4. Check for poor sensor ground terminal connection at "G" sensor electrical connector. If a problem is found, replace faulty terminal and go to step 9). If no problem is found, go to next step.
5. Check for an intermittent short to voltage in "G" sensor signal circuit between "G" sensor connector and PCM connector. If a problem is found, go to step 10). If no problem is found, go to step 8).
6. Check for an intermittent short to voltage in reference circuit between PCM and MAP sensor or "G" sensor. If a problem is found, go to step 10). If no problem is found, go to next step.
7. Check for a poor sensor ground circuit terminal connection at PCM. If a problem is found, go to step 9). If no problem is found, go to next step.
8. Check for an intermittent open or a faulty splice in sensor ground circuit. If a problem is found, go to step 10). If no problem is found, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S04195022782001010800000) .
9. Replace faulty harness connector terminal for sensor ground circuit. Retest system.
10. Locate and repair intermittent open or short circuit in wiring harness. Repair as necessary. Retest system.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. Monitor EGR actual position display while moving EGR connections and related harnesses. Change in scan tool display will indicate area of fault. Check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Turn ignition on, engine off. Using scan tool, read and record FAILS RECORD DATA. Operate vehicle within conditions noted in FAILED RECORDS DATA. Read SPECIFIC DTC. If scan tool displays DTC P1406 FAILED THIS IGN, go to next step. If scan tool does not display DTC P1406 FAILED THIS IGN, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S19759918132001010800000) .
3. Turn ignition off. Disconnect EGR valve harness connector. Inspect EGR valve and connector for damaged pins or terminals. Repair as necessary. If EGR valve and connector pins or terminals are okay, go to next step.
4. Reconnect EGR valve. Using scan tool, select MISC. TESTS, ENGINE OUTPUTS and EGR. Use up arrow to increase EGR position to 40 percent. If engine misses or stalls, go to step 14). If engine does not miss or stall, go to next step.
5. Disconnect EGR valve harness connector. Turn ignition on. Connect a test light between engine ground and EGR valve harness connector ignition feed circuit (Black/Yellow wire). If test light illuminates, go to step 7). If test light does not illuminate, go to next step.
6. Repair EGR valve ignition feed circuit open. Retest system.
7. Turn ignition off. Connect a DVOM between EGR harness connector control and ignition feed circuits. If resistance is not about 8.5 ohms, go to step 13). If resistance is about 8.5 ohms, go to next step.
8. Turn ignition on. Connect a test light between battery voltage and EGR valve harness connector control circuit (Yellow wire). If test light does not illuminate, go to step 11). If test light illuminates, go to next step.
9. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Connect a test light between battery voltage and EGR valve harness connector control circuit (Yellow wire). If test light does not illuminate, go to step 12). If test light illuminates, go to next step.
10. Locate and repair short to ground in EGR control circuit. Retest system.
11. Check EGR control circuit for an open. If no open is found, go to step 13). If an open is found, repair as necessary. Retest system.
12. Replace PCM. Retest system.
13. Replace EGR valve. If DTC P1406 still fails scan tool SPECIFIC DTC test, replace PCM. If DTC P1406 passes scan tool SPECIFIC DTC test, retest system.
14. Start engine and allow to idle. Using scan tool, select MISC. TESTS, ENGINE OUTPUTS and EGR. If pintle position voltage is .50-.75 volts, go to step 13). If pintle position voltage is .50-.75 volts, go to next step.
15. Turn ignition off. Disconnect EGR valve harness connector. Using DVOM, measure resistance between sensor ground and 5 volt reference of EGR valve. If resistance is 5000-5500 ohms, go to next step. If resistance is not 5000-5500 ohms, go to step 13).
16. Turn ignition on. Using DVOM, measure voltage between ground and 5 volt reference wire of EGR harness connector. If voltage is 4-6 volts, go to step 20). If voltage is not 4-6 volts, go to next step.
17. Backprobe for voltage between ground and PCM harness connector terminal which supplies 5 volts for EGR valve. If voltage is 4-6 volts, repair open 5 volt reference circuit. If voltage is not 4-6 volts, go to next step.
18. Check for short in EGR 5-volt reference circuit between PCM and EGR. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
19. Turn ignition off. Disconnect PCM connectors. Inspect PCM and connector for damaged pins or terminals. Repair as necessary. If PCM and connector pins and terminals are okay, replace PCM and retest system.
20. Measure voltage between EGR sensor ground and 5 volt reference wire of EGR harness connector. If voltage is 4-6 volts, go to step 23). If voltage is not 4-6 volts, go to next step.
21. Turn ignition off. Disconnect PCM connectors. Using DVOM, check for open or shorted EGR sensor ground wire between EGR and PCM. Repair as necessary. Retest system. If EGR sensor ground wire is okay, go to next step.
22. Inspect PCM and connector for damaged pins or terminals. Repair as necessary. If PCM and connector pins and terminals are okay, replace PCM and retest system.
23. Using DVOM, measure resistance between sensor ground and pintle position pin of EGR valve. If resistance is not 1000-1250 ohms, go to step 13). If resistance is 1000-1250 ohms, go to next step.
24. Turn ignition on. Connect a test light between battery voltage and EGR valve harness connector pintle position circuit (Yellow/Red wire). If test light does not illuminate, go to step 26). If test light illuminates, go to next step.
25. Turn ignition off. Disconnect PCM connectors. Leave test light connected between battery voltage and EGR valve harness connector pintle position circuit. If test light illuminates, repair short to ground in pintle position circuit (Yellow/Red wire). If test light does not illuminate, go to next step.
26. Ensure ignition is off. Disconnect PCM connectors. Turn ignition on. Using DVOM, measure voltage between ground and pintle position circuit. If voltage is zero volts, go to step 13). If voltage is not zero volts, go to next step.
27. Check for short to voltage in pintle position circuit. If short to voltage was not found, go to step 13). If short to voltage was found, repair as necessary and retest system.

An intermittent may be caused by a cracked or punctured EVAP canister, damaged or disconnected vacuum, vent or purge line. Check for poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Monitor FUEL TANK VACUUM display while moving EVAP connections and related harnesses. Change in scan tool display will indicate area 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 (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. After performing OBD system check, go to next step.
2. Remove fuel cap. Using scan tool, observe FUEL TANK VACUUM. If pressure is zero in. H2O, go to next step. If pressure is more than zero in. H2O, see FUEL TANK PRESSURE SENSOR in «SYSTEM/COMPONENT TESTS»(ref-16280) article.
3. Zero pressure and vacuum gauges on EVAP Pressure/Purge Cart (J41413). Reinstall fuel cap. Read and record FAIL RECORDS data for DTC P1441. Clear DTCs. Using scan tool, command EVAP vent solenoid ON (closed). Connect EVAP pressure/purge cart to EVAP service port. Using EVAP pressure/purge cart, attempt to pressurize EVAP system to 5 in. H2O. If specified pressure is not achieved, to step 5). If specified pressure is achieved, go to next step.
4. Maintain EVAP system pressure at 5 in. H2O. Using scan tool, read FUEL TANK VACUUM. If scan tool does not display -5 in. H2O, see FUEL TANK PRESSURE SENSOR in «SYSTEM/COMPONENT TESTS»(ref-16280) article. If scan tool displays -5 in. H2O, go to next step.
5. Disconnect vacuum source line at engine for EVAP purge solenoid. Connect a vacuum pump to EVAP canister purge valve vacuum source fitting. Apply 15 in. Hg vacuum. If vacuum does not hold, go to step 7). If vacuum holds, go to next step.
6. Check EVAP canister purge valve vacuum hoses for correct routing. If vacuum hoses are routed incorrectly, repair as necessary and go to step 8). If vacuum hoses are routed correctly, check for an intermittent problem, see «DIAGNOSTIC AIDS»(ref-16268-S00243284362001010800000) .
7. Replace EVAP canister purge valve. Retest system.
8. Start engine. Remove fuel cap. Using scan tool, command EVAP vent solenoid ON (closed) and EVAP purge solenoid OFF (0 percent). Reinstall fuel cap. Monitor scan tool FUEL TANK VACUUM display while holding engine speed at 2500 RPM. If pressure is zero in. H2O, repair is complete. If pressure is not zero in. H2O, return to last step completed and continue repair.

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Ensure air intake system is not restricted. Check throttle body for blockage and carbon build up. Clean as necessary. Inspect for a large vacuum leak at brake booster or PCV. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. After performing OBD system check, go to next step.
2. Start and idle engine. Turn off all accessories. Using scan tool, select MISC TEST, then select IAC SYSTEM. Command engine speed up to 1500 RPM, down to 500 RPM, then back to 1500 RPM while monitoring ENGINE SPEED display. If ENGINE SPEED display remains within 50 RPM of desired value, for each RPM command, fault is not present, see «DIAGNOSTIC AIDS»(ref-16268-S26287277832001010800000) . If engine speed is not within 50 RPM of desired value, go to next step.
3. Disconnect IAC valve. Install IAC Noid-Light (J 37027). Start engine. Command engine speed up to 1500 RPM, down to 500 RPM, then back to 1500 RPM while monitoring noid-light. If noid-light cycles Red and Green (never off), go to step 5). If noid-light does not cycle, go to next step.
4. Check all IAC circuits for open, short to ground or short to voltage. Repair as necessary. If circuits are okay, go to step 8).
5. Check throttle body for objects blocking IAC passage or throttle bore, excessive deposits in IAC passage, pintle, throttle bore or throttle plate. Check for restriction or vacuum leaks in air intake system. Check adjustment screw for tampering. Repair as necessary. If no problems are found, go to next step.
6. Check for poor terminal contact at IAC harness connector. Repair as necessary. If terminal contacts are okay, go to next step.
7. Replace IAC valve. Retest system.
8. Check IAC terminal contacts at PCM harness connector C1. Repair as necessary. If terminal contacts are okay, go to next step.
9. Replace PCM. Retest system.

Check for poor connection, rubbed through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Ensure air intake system is not restricted. Check throttle body for blockage and carbon build up. Clean as necessary. Check for vacuum leak. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. After performing OBD system check, go to next step.
2. Start and idle engine. Turn off all accessories. Using scan tool, select MISC TEST, then select IAC SYSTEM. Command engine speed up to 1500 RPM, down to 500 RPM, then back to 1500 RPM while monitoring ENGINE SPEED display. If ENGINE SPEED display remains within 50 RPM of desired value, for each RPM command, fault is not present, see «DIAGNOSTIC AIDS»(ref-16268-S38940971742001010800000) . If engine speed is not within 50 RPM of desired value, go to next step.
3. Disconnect IAC valve. Install IAC Noid-Light (J 37027). Start engine. Command engine speed up to 1500 RPM, down to 500 RPM, then back to 1500 RPM while monitoring noid-light. If noid-light cycles Red and Green (never off), go to step 5). If noid-light does not cycle, go to next step.
4. Check all IAC circuits for open, short to ground or short to voltage. Repair as necessary. If circuits are okay, go to step 8).
5. Check throttle body for objects blocking IAC passage or throttle bore, excessive deposits in IAC passage, pintle, throttle bore or throttle plate. Check for restriction or vacuum leaks in air intake system. Check adjustment screw for tampering. Repair as necessary. If no problems are found, go to next step.
6. Check for poor terminal contact at IAC harness connector. Repair as necessary. If terminal contacts are okay, go to next step.
7. Replace IAC valve. Retest system.
8. Replace PCM. Retest system.