Engine Controls - Tests W/codes - 3.8l Pfi Buick Regal III

INTRODUCTION

Most engine control problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoses. Before considering the computer system as a possible cause of problems, perform checks and inspections covered in BASIC TESTING article in this section. Failure to do so may result in lost diagnostic time.

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed with DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM. If no fault codes or only a non-running Code 12 is present and driveability problems exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.). If only intermittent codes are present, see INTERMITTENTS in TESTS W/O CODES article.

MODEL IDENTIFICATION

MODEL IDENTIFICATION

SELF-DIAGNOSTIC SYSTEM

Note. Electronic Control Module (ECM) may also be referred to as Powertrain Control Module (PCM) in some diagnostic charts and figures. Terms are used interchangeably.

Control module is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, control module will illuminate SERVICE ENGINE SOON light located on instrument panel. When malfunction is detected and light is turned on, a corresponding trouble code will be stored in control module memory. To retrieve stored codes, see RETRIEVING CODES (NON-SCAN) . Malfunctions are recorded as hard failures or as intermittent failures.

HARD FAILURES

Hard failures cause SERVICE ENGINE SOON light to glow and remain on until malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using diagnostic (code) charts. If a sensor fails, control module will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but it will most likely encounter degraded driveability.

INTERMITTENT FAILURES

Intermittent failures cause SERVICE ENGINE SOON light to flicker or glow and go out about 10 seconds after intermittent fault goes away. Corresponding trouble code, however, will be retained in control module memory. If related fault does not reoccur within 50 engine starts, related trouble code will be erased from control module memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article in this section.

DIAGNOSTIC PROCEDURE

Diagnosis of computerized engine control system should be performed in following order

1. Ensure all engine systems not related to computer system are operating properly. DO NOT proceed with testing unless all other problems have been repaired. DIAGNOSTIC CIRCUIT CHECK must be performed before using trouble code charts. See BASIC TESTING article in this section.
2. If trouble codes were displayed (other than Code 12), determine whether codes are hard or intermittent trouble codes. Hard codes will cause SERVICE ENGINE SOON light to glow continuously while engine is running. See «HARD OR INTERMITTENT TROUBLE CODE DETERMINATION»(/buick/regal/iii-1988-1997/remont/testing-diagnostics/#engine-controls-tests-wcodes-38l-pfi__hard-or-intermittent-trouble-code-determination) . For diagnosing hard codes, proceed to appropriate trouble code chart. For diagnosing intermittent codes, proceed to INTERMITTENTS in TESTS W/O CODES article in this section. Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes.
3. If no trouble codes were displayed and a driveability problem exists, refer to SYMPTOMS in TESTS W/O CODES article in this section. Doing so will identify proper system or component to check in I - SYS/COMP TESTS article in this section.
4. After repairs are made, clear any trouble codes and perform FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.

Note. For information on retrieving codes using a "Scan" tester, refer to user and reference manuals supplied with tester.

RETRIEVING CODES (NON-SCAN)

Note. Inserting jumper wire into test and ground terminals of ALDL connector with engine running will cause fuel injected vehicles to enter field service mode. Flashes of SERVICE ENGINE SOON light will not indicate codes if this is done. See FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.

1. Turn ignition on. DO NOT start engine. SERVICE ENGINE SOON light should glow. Locate Assembly Line Data Link (ALDL) connector attached to control module wiring harness. Most ALDL connectors are located under dash on driver side of vehicle. For exact location of ALDL, see COMPONENT LOCATIONS in I - SYS/COMP TESTS article in this section. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of ALDL connector. (Scheme 91)
2. SERVICE ENGINE SOON light should begin to flash codes. Each code will be repeated 3 times. If codes are not flashed or SERVICE ENGINE SOON light does not glow, perform DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section. To exit diagnostic mode, turn ignition off and remove jumper wire from ALDL connector.

Scheme 91

READING TROUBLE CODES

Control module stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Trouble codes may be read by counting flashes of SERVICE ENGINE SOON light or by reading digital display on a "Scan" tester. "Scan" tester is faster to use, more accurate and capable of reading information which otherwise would necessitate testing individual control module and sensor/solenoid connector terminals using a digital voltmeter. See SCAN TESTER USAGE and SCAN DATA .

Note. When using most "Scan" testers, a time delay exists between serial data updates. For instantaneous response, a digital voltmeter must be used.

If "Scan" tester is not available, reading flashes of SERVICE ENGINE SOON light is possible by grounding diagnostic test terminal "B" of ALDL with ignition on and engine off. For example, "FLASH, FLASH, pause, FLASH, longer pause" identifies Code 21. First series of flashes is first digit of trouble code. Second series of flashes is second digit of trouble code. Trouble codes are displayed starting with lowest numbered code. Each code is displayed 3 times. Codes will continue to repeat as long as ALDL test terminal is grounded.

Note. Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others require operation for 5 minutes or longer at normal operating temperature, vehicle speed and load. Therefore, some codes may not set in a service bay operational mode and may require road testing vehicle in order to duplicate condition under which code will set.

TROUBLE CODE DEFINITION

ECM/PCM TROUBLE CODE DEFINITION

Note. Use trouble code charts only if SERVICE ENGINE SOON light is illuminated (indicating a current problem exists). Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes. Anytime control module-related Codes 51, 52 or 55 are displayed with another code, start with 50-series code, and then proceed to lower numbered codes.

HARD OR INTERMITTENT TROUBLE CODE DETERMINATION

During any diagnostic procedure, determine if codes are hard failure codes or intermittent failure codes. Diagnostic charts will not usually help analyze intermittent codes. To determine hard codes and intermittent codes

1. Manually enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode, and clear trouble codes. See «CLEARING TROUBLE CODES»(/buick/regal/iii-1988-1997/remont/testing-diagnostics/#engine-controls-tests-wcodes-38l-pfi__clearing-trouble-codes) .
2. Apply parking brake, and place transmission in Neutral or Park. Block drive wheels, and start engine. SERVICE ENGINE SOON light should go out. Run warm engine at specified curb idle for 2 minutes and note SERVICE ENGINE SOON light.
3. If SERVICE ENGINE SOON light comes on, manually enter diagnostic mode. Read and record trouble codes. This will reveal hard failure codes. Codes 13, 15, 24, 44 and 45 may require a road test to reset hard failure after trouble codes were cleared.
4. If SERVICE ENGINE SOON light does not come on, all stored trouble codes were intermittent failures, except as noted above.

CLEARING TROUBLE CODES

Turn ignition switch to ON position, and ground diagnostic test terminal "B" at ALDL connector. Turn ignition switch to OFF position, and remove control module fuse from fuse block for 10 seconds. Replace fuse. Remove diagnostic terminal ground lead. If fuse cannot be located, pigtail at battery can be disconnected. When power to ECM is removed, degraded driveability may be exhibited until control module "relearns" optimum operational parameters.

ECM/PCM LOCATION

On most models, engine control module is located behind right or left side of dash or behind right or left kick panel.

Diagnostic Aids

Diagnostic aids (located in many trouble code charts) are additional tips used to help diagnose trouble codes when inspected circuit is okay. Diagnostic aids may help lead to a definitive solution to trouble code problem.

Field Service Mode Check

If ALDL test terminal "B" is grounded with engine running, SERVICE ENGINE SOON light will indicate operational mode of engine. This test confirms proper operation of fuel system and verifies "closed loop" operation. Clear codes and perform this test after any repair is completed. Field service mode check can be found by proceeding to FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.

SPECIAL TOOLS (DIAGNOSTIC)

Note. A "Scan" tester plugged into ALDL may be used to read trouble codes and check voltages in system on serial data line (terminal "E", or terminal "M" on P-4 systems). This can save a great deal of time. For additional information, see SCAN TESTER USAGE and SCAN DATA .

Computerized engine control system is most easily diagnosed using "Scan" tester; however, other tools may aid in diagnosing problems if a "Scan" tester is unavailable. These tools are a tachometer, test light, ohmmeter, digital voltmeter with 10-megohm input impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights (for both TBI and PFI) and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connectors at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.

SCAN TESTER USAGE

Note. Before connecting "Scan" tester to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received will be accurate. This is done by performing DIAGNOSTIC CIRCUIT CHECK located in BASIC TESTING article in this section. If vehicle does not pass diagnostic circuit check, information received may be invalid.

"Scan" tester is a specialized tester which, when plugged into ALDL, can be used to diagnose on-board computer control systems by providing instant access to circuit voltage information without need to crawl under dash or hood to backprobe sensors and connectors.

"Scan" tester cuts down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN DATA . They may also furnish information on output device (solenoids and motors) status. However, status parameters only indicate output signals have been sent to devices by control module; they do not indicate whether devices have responded properly to signal. Verify proper response at output device using a voltmeter or test light.

Note. Code 12 should always exist when ALDL is grounded with key on and engine not running, but it may not be indicated by all makes of "Scan" testers.

A problem may exist even if trouble codes are not present. About 80 percent of driveability problems occur without trouble codes. Sensors that are out of specification will not set a trouble code but will cause driveability problems.

Using "Scan" tester is easiest method of checking sensor specifications and other data parameters. Tester is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See SCAN DATA.

Note. If erroneous voltage signals are suspected, verify tester information using a digital voltmeter and wiring schematic. If non-existent codes are displayed, turn ignition off, remove tester, turn ignition on and ground ALDL test terminal "B". Same codes flashed by SERVICE ENGINE SOON light should be indicated by "Scan" tester.

SCAN DATA

Note. Information contained in following tables is typical of readings taken on vehicle with engine idling, upper radiator hose hot, closed throttle, transmission in Park or Neutral, "closed loop" status achieved and all accessories off (except as noted in tables). Data parameters are updated every 1 1/4 seconds. On systems using P-4 computers, parameter updates are more frequent. Not all devices and systems are used on all models; following lists only represent most commonly used parameters. For additional information, refer to owner manual furnished with tester.

PORT FUEL INJECTION

PCM/BCM CODE CHARTS

Note. In following diagnostic flow charts, schematics and illustrations are courtesy of General Motors Corp.

CODE 13, OPEN OXYGEN (O2) SENSOR CIRCUIT

CODE 13 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. This tests if problem still exists. Vehicle cannot enter "closed loop" mode if O2 sensor circuit is open. Code 13 indicates an open in O2 sensor circuit. Code will set if: Engine is at normal operating temperature. Neither Code 21 nor Code 22 is stored. O2 sensor voltage is constant within a specified range (.34-.55 volt). Throttle angle is greater than idle. A precalibrated amount of time has elapsed since start-up. All conditions have existed for a precalibrated amount of time.
2. Determines if O2 sensor, wiring or control module is at fault. If wiring is good, grounding O2 sensor wire will cause .45 volt reference supplied by control module to pull low.
3. This tests O2 sensor circuit wiring. Use only a high impedance (10-megohm minimum) digital voltmeter.

Control module will not go into closed loop if Code 13 is set. Code 13 may set if vehicle runs out of fuel or stalls while vehicle is in motion. If O2 sensor ground becomes loose, a false O2 sensor reading will occur. This can result in a Code 13 being set.

Code 13, Schematic, Open Oxygen (O2) Sensor Circuit. Scheme 92

Code 13, Flow Chart, Open Oxygen (O2) Sensor Circuit. Scheme 93

CODE 14, COOLANT TEMPERATURE SENSOR, SIGNAL VOLTAGE LOW

CODE 14 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. This chart assumes engine cooling system is functioning properly (not overheating). Test numbers refer to numbers on diagnostic chart.

1. Code 14 indicates control module has seen low coolant sensor voltage signal (high temperature) at control module terminal for a precalibrated period of time. This checks if conditions for Code 14 still exist.
2. This tests for grounded sensor signal line between control module and coolant sensor.

After engine is started, temperature should rise steadily to about 190°F (88°C) and then stabilize when thermostat opens. At normal operating temperature, signal voltage at control module terminal should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When Code 14 is set, control module will turn on electric cooling fan(s) if equipped.

Code 14, Schematic, Coolant Temp Sens Signal Voltage Low. Scheme 94

Code 14, Flow Chart, Coolant Temp Sens Signal Voltage Low. Scheme 95

CODE 14 TEMPERATURE-TO-RESISTANCE VALUES (1)

CODE 15, COOLANT TEMPERATURE SENSOR, SIGNAL VOLTAGE HIGH

CODE 15 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. Code 15 indicates control module has seen high resistance in coolant sensor circuit. This could be due to high resistance (cold temperature) or high voltage at coolant sensor terminal at control module for a precalibrated period of time. This checks if conditions for Code 15 still exist.
2. This test simulates a low voltage condition. If control module recognizes low voltage signal, "Scan" tester will display greater than 130°C. This indicates control module and wiring are not at fault.
3. This test determines if coolant sensor ground or signal circuit is open.

After engine is started, temperature should rise steadily to about 190°F (88°C) and then stabilize when thermostat opens. At normal operating temperature, voltage at control module sensor signal line should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When Code 14 is set, control module will turn on electric cooling fan(s) if equipped.

CODE 15 TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 15, Flow Chart, Coolant Temp Sens Signal Voltage High. Scheme 96

CODE 16, SYSTEM VOLTAGE HIGH/LOW

Control module monitors battery voltage on battery feed circuit. If control module detects battery voltage greater than 17.3 volts or less than 9 volts for more than 10 seconds, it will set a Code 16 in memory.

Note. Test number refers to number on diagnostic chart. Starting engine with battery charger connected may set Code 16.

1. Test alternator output to determine proper operation of voltage regulator. Increase engine speed to moderate level. Measure voltage across battery terminals. If reading is more than 17.3 volts or less than 9 volts, service alternator.

Check for poor connections or damaged harness. Also, check for an intermittent condition by starting engine and wiggling connection while monitoring battery voltage on "Scan" tester. If voltage status changes abruptly or engine stalls, check for loose connections.

Note. When Code 16 sets, transaxle will be forced to 3rd gear, preventing erratic shifting due to improper voltage.

Code 16, Schematic, System Voltage High/Low. Scheme 97

Code 16, Flow Chart, System Voltage High/Low. Scheme 98

CODE 17, RPM SIGNAL PROBLEM

Note. Test numbers refer to numbers on diagnostic chart.

1. Verifies spark reference circuit is not shorted to ground or open in ignition jumper harness.
2. If a window on harmonic balancer is lined up with 18X Hall Effect switch, ignition module will ground spark reference signal. Starter may have to be bumped several times to obtain a voltage reading.
3. Voltage reading should be lower than reading obtained with engine not running, indicating a pulsed reference signal.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a wire broken inside insulation. Also, check for backed-out connector terminals or broken insulation spark reference circuit. If everything checks okay, try wiggling related wiring harness and connectors while engine is idling. This may help to isolate location of malfunction.

Code 17, Schematic, RPM Signal Problem. Scheme 99

Code 17, Flow Chart, RPM Signal Problem. Scheme 100

CODE 21, THROTTLE POSITION SENSOR, SIGNAL VOLTAGE HIGH

CODE 21 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if code is result of a hard failure or an intermittent condition.
2. This test simulates a low-voltage condition. If control module recognizes change of state, control module and wiring are okay.
3. This step isolates a faulty sensor, control module or open sensor ground circuit. If sensor ground is shared by another sensor, an accompanying code related to that sensor may exist.

A "Scan" tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Code 21, Schematic, Throttle Position Sens, Signal Voltage High. Scheme 101

Code 21, Flow Chart, Throttle Position Sens, Signal Voltage High. Scheme 102

CODE 22, THROTTLE POSITION SENSOR, SIGNAL VOLTAGE LOW

CODE 22 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if code is result of a hard failure or an intermittent condition.
2. This test simulates conditions for a Code 21. If control module recognizes change of state, control module and wiring are okay.
3. This simulates a high signal voltage to check for an open in TPS signal line to control module. "Scan" tester should recognize this signal and display high TPS voltage.

A "Scan" tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Code 22, Flow Chart, Throttle Position Sens, Signal Voltage Low. Scheme 103

CODE 23, MAT SENSOR SIGNAL VOLTAGE HIGH

CODE 23 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. This checks if code is result of a hard failure or an intermittent condition. Code 23 will set if engine has been running for a precalibrated period of time, has reached operating temperature and signal voltage indicates a MAT temperature less than -22°F (-30°C).
2. This simulates conditions for a Code 25. If "Scan" tester displays a high temperature, control module and wiring are not at fault.
3. This checks for continuity of sensor signal and ground circuits. If ground circuit is shared by other sensors and ground circuit is open, accompanying codes related to those sensors may be present.

If engine is allowed to cool overnight, coolant and MAT sensor values should be close to each other when measured by "Scan" tester. Code 23 will result if signal and ground circuits become open. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table.

CODE 23 TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 23, Schematic, MAT Sensor Signal Voltage High. Scheme 104

Code 23, Flow Chart, MAT Sensor Signal Voltage High. Scheme 105

CODE 24, VEHICLE SPEED SENSOR (VSS)

Speed sensor, which is a Permanent Magnet (PM) generator, provides control module with vehicle speed information. PM generator, mounted in transmission, produces a pulsing AC voltage signal whenever vehicle speed is greater than 3 MPH. Voltage level and pulses increase with vehicle speed. Control module converts pulsing voltage to MPH, which is used by control module to calculate vehicle adjustments.

Note. Test numbers refer to numbers on diagnostic chart.

1. Code 24 sets when MPH reads zero, transmission is not in Park or Neutral, engine speed indicates vehicle is in a cruise mode (1200-4400) RPM, TPS indicates closed throttle and MAP sensor senses high manifold vacuum. All of these conditions must be met for 2-5 seconds. PM generator only produces a voltage signal if drive wheels are turning greater than 3 MPH.
2. Before replacing control module, PROM/MEM-CAL should be checked for correct application.

A faulty or misadjusted park/neutral switch may set a false Code 24. Use "Scan" tester to check for proper signal in Drive while wiggling shifter. Code 24 may set if vehicle is power braked (brakes applied and throttle depressed) for more than 10 seconds.

Code 24, Schematic, Vehicle Speed Sens. (VSS). Scheme 106

Code 24, Flow Chart, Vehicle Speed Sensor (VSS). Scheme 107

CODE 25, MAT SENSOR SIGNAL VOLTAGE LOW

CODE 25 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. This checks if code is hard failure or intermittent condition. Code 25 will set if a MAT temperature greater than 266°F (130°C) is sensed for more than a precalibrated period.
2. This simulates condition for Code 23. If control module recognizes open circuit and "Scan" tester displays temperature of less than -30°C, control module and wiring are okay.

If engine is allowed to cool overnight, coolant temperature sensor and MAT sensor values should be close to each other when measured by a "Scan" tester. A Code 25 will result if sensor signal circuit is shorted to ground. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table.

CODE 25 TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 25, Flow Chart, MAT Sensor Signal Voltage Low. Scheme 108

CODE 26, QUAD-DRIVER CIRCUIT (1 OF 4)

Each ECM Quad-Driver has a fault line which is monitored by ECM. ECM compares voltage values of fault line with acceptable values in ECM memory. If ECM senses values other than accepted values, a Code 26 will set.

Note. Test numbers refer to numbers on diagnostic chart.

1. ECM does not know which controlled circuit set Code 26, so chart checks each circuit to determine which is at fault. On vehicles equipped with an ECM controlled hot light, this test checks light driver and light circuit.
2. QDM symptoms: TCC inoperative, Code 39. Hot light always on, off during bulb check. Cooling fans always on low speed or will not come on at all. Poor driveability due to 100 percent canister purge.

Coolant temperature sensor, in rare cases, may fail to indicate correct coolant temperature without setting a malfunction code (Code 14 or 15). This could result in turning on hot light without having an overheating condition. It could also result in engine overheating without turning on hot light. Check coolant sensor. See COOLANT TEMPERATURE RESISTANCE TEST table in SENSOR RANGE CHARTS article in this section or Code 14 or 15 chart.

Hot Light Diagnosis

Note. These checks assume vehicle is not overheating. Verify proper operation of cooling system before diagnosing hot light.

Hot light is powered by 10-amp INDIC fuse. Light will turn on when ECM provides a ground for circuit. If circuit grounds between light and ECM, light will glow any time ignition is turned on.

1. Turn ignition on with engine off (bulb test). Go to step 3) if hot light glows. If hot light does not glow, check following: 10-amp INDIC fuse. Faulty instrument cluster bulb. Open circuit between fuse and hot light.
2. Backprobe terminal B4 at ECM using a test light to battery voltage. Turn ignition on. If test light does not glow, ECM terminal connection is bad or ECM is faulty. If test light glows, turn ignition off. Disconnect ECM connectors. Jumper terminal B4 to ground. Turn ignition on. If hot light does not glow, check for open circuit in wire between hot light and ECM. If light does not glow, all circuits are intact and power is available to light, instrument cluster must be replaced.
3. Start engine. If test light goes off, no problem is evident. See DIAGNOSTIC AIDS. If test light is on, turn ignition off. Disconnect ECM connector. Probe ECM harness terminal B4 using a test light to battery voltage. If light is off, replace ECM. If light is on, repair short to ground in circuit No. 35. If no short is present, replace instrument cluster.

Code 26, Schematic, Quad-Driver Ckt. Scheme 109

Code 26, Flow Chart, Quad-Driver Ckt (1 of 4). Scheme 110

CODE 26, QUAD-DRIVER CIRCUIT, W/ECM-CONTROLLED TEMP. LIGHT (2 OF 4)

Note. Test number refers to number on diagnostic chart.

1. 3) This determines which circuit is out of specification.

Monitor voltage of each terminal while moving related harness connectors, including ECM harness. If fault is induced, voltage will change. This may help locate intermittent problems. If code reappears with no apparent problems, replace ECM.

Code 26, Flow Chart (2 of 4) Quad-Driver Ckt, W/ECM-Controlled Temp Light. Scheme 111

CODE 26, QUAD-DRIVER CIRCUIT, W/O ECM-CONTROLLED TEMP. LIGHT (3 OF 4)

Note. Test number refers to number on diagnostic chart.

1. 3) This determines which circuit is out of specification. If all circuits are okay, in-line resistor (used in place of hot light) and related wiring should be checked. In-line resistor is taped into engine harness between right power center and ECM pigtail, about 2 inches from ECM pigtail junction.

Monitor voltage of each terminal while moving related harness connectors, including ECM harness. If fault is induced, voltage will change. This may help locate intermittent problems. If code reappears with no apparent problems, replace ECM.

Code 26, Flow Chart, Quad-Driver Ckt, W/O ECM-Controlled Temp Light, (3 of 4). Scheme 112

CODE 26, QUAD-DRIVER CIRCUIT (4 OF 4)

Note. Test number refers to number on diagnostic chart.

1. 4) This determines if problem is circuit or component. Factory-installed ECM has an internal fuse and is unlikely to need replacement.

Code 26, Flow Chart, Quad-Driver Ckt, (4 of 4). Scheme 113

CODE 27, 28 OR 29, GEAR SWITCH CIRCUITS

Gear switches are located inside transaxle. Switches are normally closed. As vehicle speed increases, hydraulic pressure applies specific gear clutches and gear switch opens. ECM uses gear switches to help determine control of fuel delivery and TCC operation.

Code 27 sets if Code 29 is not present, 2nd gear signal circuit indicates ground or closed switch for 10 seconds when vehicle is in 4th gear, or 2nd gear or 4th gear circuits indicate an open when engine is first started.

Code 28 sets if 3rd gear circuit indicates ground or closed switch for 10 seconds when vehicle is in 4th gear or if 3rd gear or 4th gear circuit indicates an open when engine is first started.

Code 29 sets if 4th gear circuit indicates ground or closed switch for 10 seconds when vehicle is in 4th gear (TCC locked and brake not applied) or if 4th gear circuit indicates an open when engine is first started.

Note. Test numbers refer to numbers on diagnostic chart.

1. A digital volt-ohmmeter must be used in this test. A test light will not work due to low voltage supplied by ECM.
2. Checks if circuit is grounded through switch.
3. Checks for a good, properly operating switch and checks circuit within transaxle for an improper ground.

Check for poor connections at ECM pins. Inspect harness for incorrect routing (too close to high voltage wiring) and chafing. Monitor voltage of each terminal while moving related harness connectors. If failure is induced, voltage reading will change.

CODE 31, PARK/NEUTRAL SWITCH CIRCUIT

Park/neutral switch contacts are part of neutral start switch. Contacts close to ground in Park or Neutral and open in Drive. Code 31 will set if park/neutral signal circuit indicates an open for 3-4 consecutive starts or if conditions occur as follows

1. Code 29 does not exist.
2. Circuit No. 434 indicates ground.
3. Transmission is in high gear.
4. TCC is locked (4T60 transaxle).
5. TPS is less than 15 percent (.94 volt) and vehicle speed is greater than 45 MPH (3T40 transaxle).
6. All above conditions have been met for at least 12 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. This tests for a closed switch to ground in Park.
2. This tests for an open switch in Drive.
3. Be sure "Scan" tester indicates Drive, even when wiggling shifter.

Code 31, Schematic, Park/Neutral Switch Ckt. Scheme 114

Code 31, Flow Chart, Park/Neutral Switch Ckt. Scheme 115

CODE 34, MAF SENS, SIGNAL VOLTAGE LOW

Code 34 is set when engine is running without MAF sensor signal for greater than 4 seconds. If Code 34 is set, control module will substitute a value for MAF based upon RPM, TPS and IAC monitored parameters.

Note. Test numbers refer to numbers on diagnostic chart.

1. Determines if code is result of an intermittent or hard failure.
2. Voltage reading at sensor harness terminal "A" of less than 4 volts or more than 6 volts indicates fault in circuit No. 492 or poor connections.
3. Verifies both ignition voltage and a good ground are available.

MAF sensor produces a frequency signal, which cannot be easily measured. Check for following

1. Poor Connections Inspect control module MAF signal pins and harness connectors for backed-out terminals, improper connector mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connection.
2. Harness Inspect MAF sensor harness to ensure it is not too close to high voltage wires, such as spark plug wires.
3. Intermittents If harness appears okay, use "Scan" tester to check MAF while moving related connectors and wiring harness. A change in display would indicate intermittent fault location.

Code 34, Schematic, MAF Sens, Signal Voltage Low. Scheme 116

Code 34, Flow Chart, MAF Sens, Signal Voltage Low. Scheme 117

CODE 35, IAC IDLE SPEED ERROR, W/O TECH 1

Code 35 will set when closed throttle engine speed is 150 RPM greater or less than correct idle speed for 20 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. IAC driver is used to extend and retract IAC valve. Movement is verified by an engine speed change. If no change in speed occurs, valve can be retested when removed from throttle body.
2. Checks IAC movement quality from step 1). Between 700-1500 RPM, engine speed should change smoothly with each flash of tester light in both extend and retract. If IAC valve is retracted beyond control range (about 1500 RPM), many flashes in extend position may occur before engine speed begins to drop. This is normal on certain engines. Fully extending IAC may cause engine to stall. This may be normal.
3. Steps 1) and 2) verified proper IAC valve operation while this step checks IAC circuits. Each light on node light should flash red and green while IAC valve is cycled. While sequence of color is not important, check circuits for faults beginning with poor terminal contacts if either light is off or does not flash red and green.

A slow, unstable idle may be caused by a system problem which cannot be overcome by IAC. "Scan" counts will be greater than 60 if idle is too low and zero counts if idle is too high. If idle is too high, stop engine. Fully extend IAC using driver. Start engine. If idle speed is greater than 800 RPM, look for possible vacuum leaks.

System Too Lean

If air/fuel ratio is too lean, idle speed may be either too high (check for vacuum leaks) or too low. Engine speed may vary up and down; disconnecting IAC may not help. "Scan" and/or digital voltmeter (10-megohm) will read an oxygen (O2) sensor output less than 300 mv (.3 volt). Check for low fuel pressure or water in fuel. A contaminated O2 sensor (caused by silicone) will produce lean air/fuel mixtures with an O2 sensor output fixed greater than 800 mv (.8 volt). This may also set Code 45.

System Too Rich

If air/fuel ratio is too rich, idle speed will be too low and "Scan" tester counts will usually be greater than 80. System may be obviously rich, with black smoke from exhaust pipe. "Scan" tester and/or voltmeter will read an O2 sensor voltage signal fixed greater than 800 mv (.8 volt). Look for high fuel pressure and injectors leaking or sticking. Remove IAC, and inspect bore for foreign material and evidence of IAC valve dragging bore.

Throttle Body

Remove IAC, and inspect bore for evidence of IAC valve dragging.

IAC Valve Connections

Inspect carefully for loose or corroded connections.

PCV Valve

An incorrect PCV valve may cause incorrect idle speed.

Code 35, Schematic, IAC Idle Speed Error, W/O Tech 1. Scheme 118

Code 35, Flow Chart, IAC Idle Speed Error, W/O Tech 1. Scheme 119

CODE 35, IAC IDLE SPEED ERROR, USING TECH I

Code 35 will set when closed throttle engine speed is 150 RPM greater or less than correct idle speed for 20 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. Tech 1 RPM control mode is used to extend and retract IAC valve. Movement is verified by an engine speed change. If no change in speed occurs, valve can be retested when removed from throttle body. If IAC valve is retracted beyond control range (about 1500 RPM), many flashes in extend position may occur before engine speed begins to drop. This is normal on certain engines. Fully extending IAC may cause engine to stall. This may be normal.
2. This test uses Tech 1 to command IAC-controlled idle speed. Control module issues commands to obtain requested idle speed. Each light on node light should flash red and green while IAC valve is cycled. While sequence of color is not important, check circuits for faults beginning with poor terminal contacts if either light is off or does not flash red and green.

A slow, unstable idle may be caused by a system problem which cannot be overcome by IAC. "Scan" counts will be greater than 60 if idle is too low and zero counts if idle is too high. If idle is too high, stop engine. Fully extend IAC with driver. Start engine. If idle speed is greater than 800 RPM, look for possible vacuum leaks.

If air/fuel ratio is too lean, idle speed may be either too high (check for vacuum leaks) or too low. Engine speed may vary up and down; disconnecting IAC may not help. "Scan" and/or digital voltmeter (10-megohm) will read an oxygen (O2) sensor output less than 300 mv (.3 volt). Check for low fuel pressure or water in fuel. A contaminated O2 sensor (caused by silicone) will produce lean air/fuel mixtures with an O2 sensor output fixed greater than 800 mv (.8 volt). This may also set Code 45.

If air/fuel ratio is too rich, idle speed will be too low and "Scan" tester counts will usually be greater than 80. System may be obviously rich, with black smoke from exhaust pipe. "Scan" tester and/or voltmeter will read an O2 sensor voltage signal fixed greater than 800 mv (.8 volt). Look for high fuel pressure and injectors leaking or sticking. Remove IAC, and inspect bore for foreign material and evidence of IAC valve dragging bore.

Remove IAC, and inspect bore for evidence of IAC valve dragging.

Inspect carefully for loose or corroded connections.

An incorrect PCV valve may cause incorrect idle speed.

Code 35, Flow Chart, IAC Idle Speed Error, Using Tech I. Scheme 120

CODE 38, BRAKE SWITCH CIRCUIT

Code 38 will set if Code 24 is not present, status at brake input terminal of control module has not changed from high to low and vehicle speed has been greater than 35 MPH and back to zero MPH a precalibrated number of times.

Note. Test numbers refer to numbers on diagnostic chart.

1. Jumpering brake switch determines if ECM and wiring for brake switch are okay.
2. Determines if brake switch is out of adjustment or is faulty.
3. Verifies voltage to brake switch.

A Code 38 in conjunction with a Code 39 or 26 would mean a problem with one or more of following components

1. Fuse or power supply circuit, brake switch or wire before splice.
2. Code 38 alone is result of a wire or circuit problem between splice and control module, poor connection to control module, or possibly control module itself.

If brake switch has failed in an open state, TCC will not engage. Code 38 does not turn on SERVICE ENGINE SOON light on all models.

Code 38, Schematic, Brake Switch Ckt. Scheme 121

Code 38, Flow Chart, Brake Switch Ckt. Scheme 122

Note. Scan testers display brake status in different manners depending upon manufacturer. What is important is that status changes when brake pedal is depressed.

CODE 39, TCC CIRCUIT, W/O TECH 1, W/4T60 TRANSAXLE

Code 39 will set when Codes 28 and 29 are not set, brake is not applied, TCC is commanded by ECM, transmission is in high gear and engine speed-to-vehicle speed ratio does not indicate TCC has engaged. All these conditions must have been met for more than 15 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. Tests fuse, brake switch and battery power circuit to TCC solenoid.
2. Tests for ECM driver operation at TCC harness connector.
3. Tests for ECM driver operation at ECM terminal.

A Code 39 in conjunction with a Code 38 would mean a problem with one or more of following components

1. Fuse or power circuit, brake switch or wire before splice.

Code 39 alone indicates a problem at

1. Brake input circuit between splice and TCC solenoid.
2. TCC drive circuit between TCC solenoid and ECM.
3. Poor connection to ECM or ECM itself.

Code 39, TCC Ckt, Flow Chart, W/4T60 Transaxle. Scheme 123

CODE 39, TCC CIRCUIT USING TECH 1, W/4T60 TRANSAXLE

Code 39 will set when Codes 28 and 29 are not set, brake is not applied, TCC is commanded by ECM, transmission is in high gear and engine speed-to-vehicle speed ratio does not indicate TCC has engaged. All these conditions must have been met for more than 15 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. Tests fuse, brake switch and battery power circuit to TCC solenoid.
2. Tests for ECM driver operation at TCC harness connector.
3. Tests for ECM driver operation at ECM terminal.

A Code 39 in conjunction with a Code 38 would mean a problem with one or more of following components

1. Fuse or power circuit, brake switch or wire before splice.

1. Brake input circuit between splice and TCC solenoid.
2. TCC drive circuit between TCC solenoid and ECM.
3. Poor connection to ECM or ECM itself.

Code 39, TCC Ckt, Flow Chart, W/4T60 Transaxle. Scheme 124

CODE 41, CAM SENSOR CIRCUIT

Code 41 will set if engine is running and a cam sensor signal is not received by ECM for last 2 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. Verifies proper operation of circuits No. 633, 644 and 645.
2. Tests circuit No. 630 from C(3)I module to ECM.
3. If camshaft gear magnet is interfacing with cam sensor, voltage reading will be zero. Bumping engine will cause condition to go away.
4. If voltage reading is constantly varying around a midpoint of 4.6 volts and connections are good, ECM is faulty.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a wire broken inside insulation. Check for following

1. Poor Connection Inspect ECM harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
2. Intermittents If connections and harness are okay, connect a digital volt-ohmmeter (10-megohm) between ECM terminal R10 and ground. Monitor DVOM while moving related connectors and wiring harness. Voltage reading will change if failure is induced. This may help isolate malfunction.

Code 41, Schematic, Cam Sens Ckt. Scheme 125

Code 41, Flow Chart, Cam Sens Ckt. Scheme 126

Note. Ensure battery is fully charged. If code is intermittent, see Diagnostic Aids. If engine will not start, see NO START Diagnosis in Basic Diagnostic Procedures article.

CODE 42, EST CIRCUIT OPEN OR GROUNDED

Note. For applicable schematic, see previous page.

Code 42 will set if EST or by-pass circuit is open or grounded at time of engine start-up.

Note. Test numbers refer to numbers on diagnostic chart.

1. Tests if ECM recognizes a problem. If ECM does not set Code 42 at this point, problem is intermittent. Check for a loose connection.
2. With ECM disconnected, digital volt-ohmmeter should indicate less than 200 ohms. This is normal EST circuit resistance through ignition module. A higher resistance would indicate a fault in circuit No. 423, a poor ignition module connection or a faulty ignition module.
3. If test light was on when connected from 12 volts to ECM harness by-pass circuit, either circuit No. 424 is shorted to ground or ignition module is faulty.
4. Tests if ignition module switches when by-pass circuit is energizedby 12 volts through test light. If ignition module switches, resistance reading should switch from less than 200 ohms to more than 6000 ohms.
5. Disconnecting ignition module should make ohmmeter indicate as if it were monitoring an open circuit (infinite reading). Otherwise, circuitNo. 423 is shorted to ground.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a wire broken inside insulation. Inspect ECM harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.

If connections and harness are okay, connect a digital volt-ohmmeter between affected terminal to ground, and monitor meter while moving related connectors and wiring harness. If failure is induced, voltage reading will change.

Code 42, Flow Chart, EST Ckt Open or Grounded. Scheme 127

CODE 43, ESC ERROR, W/O ESC MODULE

Note. Test numbers refer to numbers on diagnostic chart. If an audible knock is heard from engine at idle, repair internal engine problems before proceeding.

1. If tapping on engine does not produce a knock signal on "Scan" tester, try tapping engine closer to sensor before proceeding.
2. ECM supplies a 5-volt reference signal on knock sensor line. With knock sensor connected, this signal is pulled low to about 2.5 volts. Knock signal, which is an AC signal, rides on this 2.5-volt DC signal.
3. This test determines if knock sensor is faulty or if ESC portion of MEM-CAL is faulty.

Check knock sensor signal circuit for a potential open or short to ground. An open knock signal circuit would cause 5-volt reference to remain high at ECM knock signal terminal. A short to ground in knock signal circuit would cause 5-volt reference signal to pull low to near zero volts. Resistance to ground through knock sensor should be 3300-4500 ohms. Also check for proper installation of MEM-CAL.

Code 43, Schematic, ESC Error, W/O ESC Module. Scheme 128

Code 43, Flow Chart, ESC Error, W/O ESC Module. Scheme 129

CODE 44, LEAN EXHAUST INDICATION

CODE 44 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

O2 sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600°F (316°C). An open sensor circuit or cold sensor causes "open loop" operation.

Note. Test number refers to number on diagnostic chart.

1. Checks to see if O2 sensor is registering a lean condition. Code 44 is set when O2 sensor voltage signal at control module is low (less than .3 volt) for a precalibrated period and system is operating in "closed loop".

Using "Scan" tester, observe Block Learn Memory (BLM) value at different RPMs. If conditions for a Code 44 exist, block learn value will be about 150.

O2 Sensor Wire

O2 sensor wire may be mispositioned and laying against exhaust manifold. Check for ground between sensor and wire connector.

Fuel Contamination

Water, even small amounts, near in-tank fuel pump inlet can be delivered to injector. Water may cause a lean exhaust and set Code 44.

Fuel Pressure

System will be lean if fuel pressure is low. If necessary, monitor fuel pressure while driving vehicle. For fuel pressure checking procedure, see BASIC TESTING article in this section.

Exhaust Leaks

If exhaust system has large leaks, exhaust system negative pressure pulses can cause outside air to be drawn into system and past O2 sensor. Vacuum or crankcase leaks can also cause a lean condition.

Misfire Or Stall

If engine misfires or stalls (including running out of fuel) while vehicle is moving, a Code 44 may set. If Code 44 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Code 44, Flow Chart, Lean Exhaust Indication. Scheme 130

CODE 45, RICH EXHAUST INDICATION

CODE 45 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

O2 sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600°F (316°C). An open sensor circuit or cold sensor causes "open loop" operation.

Code 45 indicates a rich exhaust. Diagnosis should begin with fuel pressure, leaking injector, HEI shielding (ground), vapor canister fuel saturation, coolant sensor, MAP sensor, O2 sensor contamination and TPS intermittent output.

Note. Test number refers to number on diagnostic chart.

1. Test checks to see if O2 sensor is registering a rich condition. Code 45 is set when vehicle is at operating temperature (in "closed loop"), throttle angle is greater than idle, O2 sensor signal at control module is greater than .7 volt for a precalibrated period and time since engine start is one minute or more.

If other codes of lower number are set with Code 45, use those charts first. Malfunction in MAP or TPS sensor circuits can cause a Code 45 to set. If other codes are not set, Code 45, rich exhaust, is most likely caused by

Fuel Pressure High

If fuel pressure is too high, air/fuel ratio will be rich. For fuel pressure checking procedure, see BASIC TESTING article in this section. Control module can compensate for slight increases, but a Code 45 will be set if air/fuel ratio becomes too rich.

Ignition Ground

If an open occurs on HEI ground circuit, HEI induced electrical "noise" may result, causing simulated reference pulses to be picked up by control module on reference line of EST harness. Additional pulses result in a higher than actual engine speed signal. Control module will increase injector pulse width ("on" time) to match increased RPM signal. "Scan" tester will show higher than actual RPM, which can help in diagnosing this problem.

Evaporative Fuel Canister

Fuel saturation of charcoal canister will cause a rich air/fuel ratio. If canister is full of fuel, check canister control valves and hoses.

MAP Sensor

An output causing control module to sense a higher than normal manifold pressure (low vacuum) can cause system to go rich. Disconnecting MAP sensor will allow control module to substitute a fixed value for MAP sensor. If condition disappears, substitute a different MAP sensor, and continue testing.

TPS

An intermittent TPS output will cause system to operate rich due to a false indication of engine acceleration.

O2 Sensor Contamination

O2 sensor contamination, caused by silicone in certain fuels or use of improper RTV sealant, may cause a white powdery coating to cover exterior of O2 sensor. False high signal voltage (low oxygen content sensed) produced is interpreted by control module as a rich mixture, causing control module to set Code 45.

EGR Problem

EGR valve sticking open at idle is usually accompanied by a rough idle and/or stalling.

Also check for shorted or leaking injector and fuel-contaminated oil. If Code 45 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Code 45, Flow Chart, Rich Exhaust Indication. Scheme 131

CODE 48, MISFIRE DIAGNOSIS

Note. If multiple codes are present, go to lowest code first. Repairing Code 13, 44 or 45 may correct Code 48.

Code 48 will set if TPS is .48-1.30 volts, RPM is 1300-2100, MPH is 50-60, O2 sensor cross counts are greater than 21 and all of these conditions are met for 30 seconds.

Ignition System Checks - Remove and inspect each spark plug. If plugs are fouled, check ignition wires, ignition coil and ignition module operation. If plugs are cracked or worn, replace plugs. If no fault is found, perform BASIC ENGINE CHECKS.

Fuel System Checks

Check for restricted fuel system (injectors, fuel pump, lines and filter). Perform PFI INJECTOR BALANCE TEST. See I - SYS/COMP TESTS article in this section. Verify proper injector circuit operation using Injector Tester (J-34730-3). Check fuel pump pressure and volume.

Basic Engine Checks

Check engine compression. Unless spark plug condition or compression check identifies a specific cylinder, road test vehicle under test conditions to verify Code 48 before engine disassembly. Upon disassembly, inspect pistons, rings, valves, valve springs and valve guides. Check for worn or damaged camshaft lobes and lifters.

Code 48, Flow Chart, Misfire Diagnosis. Scheme 132

CODE 51, FAULTY PROM/MEM-CAL

Ensure all pins are fully inserted in socket. If pins are okay, replace PROM/MEM-CAL, clear memory and recheck. If Code 51 reappears, replace control module.

CODE 52, FAULTY CAL-PAK

Ensure all pins are fully inserted in socket. If pins are okay, replace CAL-PAK, clear memory and recheck. If Code 51 reappears, replace control module.

CODE 66, LOW A/C REFRIGERANT CHARGE, (W/O DIGITAL DISPLAY)

ECM monitors A/C request and completes ground for A/C relay when an A/C mode is selected at control head and refrigerant pressure is sufficient to close pressure cycling switch. If A/C pressure is low and clutch cycles too often, ECM will protect compressor by disabling A/C relay and setting Code 66. Relay will be disabled until next ignition cycle. If Code 66 is set during 3 consecutive ignition cycles, A/C relay will be disabled until Code 66 is cleared from memory. Code 66 does not illuminate SERVICE ENGINE SOON light. Code 66 will set if A/C request signal lasts less than 1.5 seconds for 10 or more consecutive compressor "on" cycles within a 15 minute period.

Note. Test numbers refer to numbers on diagnostic chart.

1. A stored Code 66 may not allow compressor to engage if it has been present during last 3 ignition cycles. Ensure code has been cleared before attempting diagnosis.
2. Pressure varies greatly depending upon temperature.

Code 66, Schematic, Low A/C Refrigerent Charge. Scheme 133

Code 66, Flow Chart, Low A/C Refrigerant Charge (W/O Digital Display). Scheme 134

CODE 69, A/C HEAD PRESSURE SWITCH

A/C head pressure switch closes to ground at 210 psi (14.77 kg/cm 2 ). When switch is closed, fans should run at high speed. If Code 69 is set, engine cooling fans will run at high speed anytime A/C is requested.

Code 69, Schematic, A/C Head Pressure Switch. Scheme 135

Code 69, Flow Chart, A/C Head Pressure Switch. Scheme 136

SUMMARY

If no hard fault codes are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

See also:
• RETRIEVING CODES (NON-SCAN)
• HARD OR INTERMITTENT TROUBLE CODE DETERMINATION
• SCAN TESTER USAGE
• SCAN DATA
• CLEARING TROUBLE CODES