Engine Controls - Tests W/codes - 3.8l Buick Park Avenue I

INTRODUCTION

Note. This article does not apply to the BCM function on Riviera. For information on this system, see G - PCM/BCM TESTS W/CODES article in this section.

Note. This article does not apply to the BCM function on Riviera. For information on this system, see G - PCM/BCM TESTS W/CODES article in this section.

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 TESTING , 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 in this section.

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. SERVICE ENGINE SOON light may also be referred to as the Malfunction Indicator Light (MIL). 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/park-avenue/i-1991-1996/remont/testing-diagnostics/#engine-controls-tests-wcodes-38l__hard-or-intermittent-trouble-code-determination) . For diagnosing hard codes, proceed to appropriate trouble code chart. For diagnosing intermittent codes, proceed to INTERMITTENTS in BASIC TESTING 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 necessary repairs are made, clear 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. On Riviera, codes can also be retrieved through Electronic Climate Control Panel (ECCP). For additional information on Riviera ECCP function, see G - PCM/BCM TESTS W/CODES article in this section.

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 154)
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 154

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. (Scheme 154) 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/park-avenue/i-1991-1996/remont/testing-diagnostics/#engine-controls-tests-wcodes-38l__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. (Scheme 154) 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. On Grand Prix and Lumina, control module is located on right side of engine compartment. See COMPONENT LOCATIONS in I - SYS/COMP TESTS article in this section.

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 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.

SCAN DATA - PORT FUEL INJECTION

ECM/PCM CODE CHARTS

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

CODE 13 - OPEN OXYGEN SENSOR CIRCUIT

Note. Test numbers refer to numbers on diagnostic chart.

1. This tests if problem still exists. Vehicle cannot enter "closed loop" mode if oxygen 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, oxygen 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 and all conditions have existed for a precalibrated amount of time.
2. Determines if oxygen sensor, wiring or control module is at fault. If wiring is good, grounding oxygen sensor wire will cause .45 volt reference supplied by control module to pull low.
3. This tests oxygen 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 oxygen sensor ground becomes loose, a false oxygen sensor reading will occur. This can result in a Code 13 being set. On models equipped with an oxygen sensor heating element, element resistance should be 3.5-14 ohms.

CODE 13 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 13 Schematic (All Models) Open Oxygen Sensor Circuit. Scheme 155

Code 13 Flow Chart (All Models) Open Oxygen Sensor Circuit. Scheme 156

CODE 14 - COOLANT TEMPERATURE SENSOR (SIGNAL VOLTAGE LOW)

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 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 14 Schematic (Signal Voltage Low) Coolant Temperature Sensor. Scheme 157

Code 14 Flow Chart (Signal Voltage Low) Coolant Temperature Sensor. Scheme 158

CODE 15 - COOLANT TEMPERATURE SENSOR (SIGNAL VOLTAGE HIGH)

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 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 15 Flow Chart (Signal Voltage High) Coolant Temperature Sensor. Scheme 159

CODE 16 - SYSTEM VOLTAGE HIGH/LOW (3.8L)

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 Flow Chart (3.8L) System Voltage High/Low. Scheme 160

CODE 17 - RPM SIGNAL PROBLEM (3.8L)

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 (3.8L (VIN L) "C" & "H" Bodies) RPM Signal Problem. Scheme 161

Code 17 Schematic (3.8L (VIN 1) "C" & "H" Bodies) RPM Signal Problem. Scheme 162

Code 17 Schematic (3.8L "E" Body) RPM Signal Problem. Scheme 163

Code 17 Schematic (3.8L "W" Body) RPM Signal Problem. Scheme 164

Code 17 Flow Chart (3.8L) RPM Signal Problem. Scheme 165

CODE 18 - CAM/CRANK ERROR (3.8L "C", "H" & "W" BODIES)

During cranking, ignition module monitors dual crank sensor sync signal. Sync signal is used to determine correct cylinder pair to spark first. After sync signal has been processed by ignition module, module sends a fuel control reference pulse to PCM. When PCM receives this pulse, it will command all 6 injectors to fire for one priming shot of fuel. After priming, all injectors are held off for 2 crankshaft revolutions to allow cylinder to use fuel from priming shot. After firing, PCM begins to operate injectors in sequential mode based upon true camshaft position. PCM expects to see 6 fuel control pulses for each cam pulse. If sequence of these pulses is incorrect 10 times consecutively, Code 18 will set.

Note. Test numbers refer to numbers on diagnostic chart.

1. Determines if conditions necessary to set code still exist.
2. If 5 volts are not present at PCM harness connector terminal, cam sensor may be interfacing with magnet in camshaft sprocket. Bumping starter should correct this problem.
3. If a failure is induced in fuel control reference circuit, 5 volts on circuit should change when faulty wiring or connection is manipulated.

Code 18 indicates an intermittent fault and may not set immediately or under all conditions. Symptoms experienced may help isolate cause of condition. A poor connection or fault in any cam sensor circuit or a faulty cam sensor may cause PCM to re-initialize injector sequence, causing a possible stumble or miss. A poor connection or fault in any crank sensor circuit or fuel control circuit or bent or missing vanes on harmonic balancer interrupter rings will cause PCM to stop pulsing injectors when fault occurs. This will cause an intermittent stumble or stall.

Code 18 Flow Chart (3.8L "C", "H" & "W" Bodies) CAM/CRANK Error. Scheme 166

CODE 21 - THROTTLE POSITION SENSOR (SIGNAL VOLTAGE HIGH)

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 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 21 Schematic (All Models) Throttle Position Sensor (Signal Voltage High). Scheme 167

Code 21 Flow Chart (All Models) Throttle Position Sensor (Signal Voltage High). Scheme 168

CODE 22 - THROTTLE POSITION SENSOR (SIGNAL VOLTAGE LOW)

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 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 22 Flow Chart (All Models) Throttle Position Sensor (Signal Voltage Low). Scheme 169

CODE 23 - MAT SENSOR (SIGNAL VOLTAGE HIGH)

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 intake air 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 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 23 Schematic MAT Sensor (Signal Voltage High). Scheme 170

Code 23 Flow Chart MAT Sensor (Signal Voltage High). Scheme 171

CODE 24 - VEHICLE SPEED SENSOR (3.8L "W" BODY)

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 (3.8L "W" Body) Vehicle Speed Sensor. Scheme 172

Code 24 Flow Chart (3.8L "W" Body) Vehicle Speed Sensor. Scheme 173

CODE 24 - VEHICLE SPEED SENSOR (3.8L "C", "E" & "H" BODIES)

Note. Test numbers refer to numbers on diagnostic chart.

Scheme 174

Scheme 175

1. Code 24 will set if vehicle speed is less than 3 MPH when engine is running, Code 29 and 31 are not set, vehicle is in 4th gear and all conditions have been met for 2-40 seconds.
2. Before replacing control unit, check MEM-CAL for correct application. (Scheme 174): Code 24 Schematic (3.8L "C", "E" & "H" Bodies) Vehicle Speed Sensor (Scheme 175): Code 24 Flow Chart (3.8L "C", "E" & "H" Bodies) Vehicle Speed Sensor

CODE 25 - MAT SENSOR (SIGNAL VOLTAGE LOW)

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 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 25 Flow Chart MAT Sensor (Signal Voltage Low). Scheme 176

CODE 26 - QUAD-DRIVER "A" (3.8L "C" & "H" BODIES) (1 OF 3)

PCM controls most components with electronic switches completing a ground circuit when actuated. Switches are arranged in groups of 4, called Quad-Driver Modules (QDMs), which can independently control up to 4 outputs (control module terminals). When an output is actuated, terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage will normally be high.

QDMs are fault-protected. If a relay or solenoid coil is shorted (having very low resistance) or if control side of circuit is shorted to voltage, too much current would be allowed into QDM. QDM senses this and turns driver off or QDM's internal resistance increases to limit current flow and protect QDM. Result is high output terminal voltage when it should be low. If circuit from battery voltage or component is open or control side of circuit is shorted to ground, terminal voltage will be low, even when output is turned off. Either of these conditions is considered to be a QDM fault.

Each QDM has a separate fault line to indicate presence of a current fault to control module central processor. A scan tester displays status of each of these fault lines as "low equals okay" or "high equals fault".

Note. Test numbers refer to numbers on diagnostic chart.

Scheme 177

Scheme 178

1. The PCM does not know which controlled circuit caused code to set. This chart will go through each of the circuits to determine which is at fault. This test checks the SERVICE ENGINE SOON light driver circuit.
2. QDM-related codes include Codes 38 and 39. QDM symptoms include: TEMP light on all the time, off during bulb check, cooling fan on low speed all the time or won't come on at all, poor driveability due to 100 percent canister purge and TCC does not engage. (Scheme 177): Code 26 Schematic (3.8L "C" & "H" BODIES) Quad-Driver "A" Error (Scheme 178): Code 26 Flow Chart (3.8L "C" & "H" BODIES) (1 of 3) Quad-Driver "A" Error

CODE 26 - QUAD-DRIVER "A" (3.8L "C" & "H" BODIES) (2 OF 3)

Note. Test numbers refer to numbers on diagnostic chart.

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

Monitor voltage at each terminal while wiggling related harness connectors, including PCM harness. If the failure is induced, voltage will change. If no faults are found and code resets for no apparent reason, replace PCM.

Code 26 Flow Chart (3.8L "C" & "H" BODIES) (2 of 3) Quad-Driver "A" Error. Scheme 179

CODE 26 - QUAD-DRIVER "A" (3.8L "C" & "H" BODIES)(3 OF 3)

Note. Test numbers refer to numbers on diagnostic chart.

Scheme 180

1. 4) This test will determine if the problem is the circuit or the component. As the factory installed PCM is protected by an internal circuit breaker, it is unlikely that the PCM needs to be replaced. (Scheme 180): Code 26 Flow Chart (3.8L "C" & "H" BODIES) (3 of 3) Quad-Driver "A" Error

CODE 26 - QUAD-DRIVER ERROR (3.8L "E" BODY)(1 OF 3)

PCM controls most components with electronic switches completing a ground circuit when actuated. Switches are arranged in groups of 4, called Quad-Driver Modules (QDMs), which can independently control up to 4 outputs (control module terminals). When an output is actuated, terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage will normally be high.

QDMs are fault-protected. If a relay or solenoid coil is shorted (having very low resistance) or if control side of circuit is shorted to voltage, too much current would be allowed into QDM. QDM senses this and turns driver off or QDM's internal resistance increases to limit current flow and protect QDM. Result is high output terminal voltage when it should be low. If circuit from battery voltage or component is open or control side of circuit is shorted to ground, terminal voltage will be low, even when output is turned off. Either of these conditions is considered to be a QDM fault.

Each QDM has a separate fault line to indicate presence of a current fault to control module central processor. A scan tester displays status of each of these fault lines as "low equals okay" or "high equals fault". Code 26 will set if the engine is running and PCM detects an improper voltage level on a circuit connected to a QDM for more than 5 seconds.

For QDM "A" to set a Code 26, the brake switch must be closed (brakes not applied). Some QDM circuits will normally switch between high and low. Some scan testers may cause a false Code 26 to set if the engine is running and the service brake is depressed for greater than 30 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

Scheme 181

Scheme 182

1. The PCM does not know which controlled circuit caused code to set. This chart will go through each of the circuits to determine which is at fault. This test checks the SERVICE ENGINE SOON light driver circuit. QDM symptoms include: cooling fan on low speed all the time or won't come on at all, poor driveability due to 100 percent canister purge, improper transaxle shifting and harsh TCC engagement or TCC does not engage. (Scheme 181): Code 26 Schematic (3.8L "E" Body) Quad-Driver Error (Scheme 182): Code 26 Flow Chart (3.8L "E" Body)(1 of 3) Quad-Driver Error

CODE 26 - QUAD-DRIVER ERROR (3.8L "E" BODY)(2 OF 3)

Note. Test numbers refer to numbers on diagnostic chart.

1. 2) This test determines which circuit is out of specification.

Monitor voltage at each terminal while wiggling related harness connectors, including PCM harness. If the failure is induced, voltage will change. If no faults are found and code resets for no apparent reason, replace PCM.

Code 26 Flow Chart (3.8L "E" Body)(2 of 3) Quad-Driver Error. Scheme 183

CODE 26 - QUAD-DRIVER ERROR (3.8L "E" BODY)(3 OF 3)

Note. Test numbers refer to numbers on diagnostic chart.

1. 3) This test will determine if the problem is the circuit or the component. As the factory installed PCM is protected by an internal circuit breaker, it is unlikely that the PCM needs to be replaced.

Code 26 Flow Chart (3.8L "E" Body)(3 of 3) Quad-Driver Error. Scheme 184

CODE 26 - QUAD-DRIVER "A" ERROR (3.8L "W" BODY) (1 OF 4)

PCM controls most components with electronic switches completing a ground circuit when actuated. Switches are arranged in groups of 4, called Quad-Driver Modules (QDMs), which can independently control up to 4 outputs (control module terminals). When an output is actuated, terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage will normally be high.

QDMs are fault-protected. If a relay or solenoid coil is shorted (having very low resistance) or if control side of circuit is shorted to voltage, too much current would be allowed into QDM. QDM senses this and turns driver off or QDM's internal resistance increases to limit current flow and protect QDM. Result is high output terminal voltage when it should be low. If circuit from battery voltage or component is open or control side of circuit is shorted to ground, terminal voltage will be low, even when output is turned off. Either of these conditions is considered to be a QDM fault.

Each QDM has a separate fault line to indicate presence of a current fault to control module central processor. A scan tester displays status of each of these fault lines as "low equals okay" or "high equals fault". Code 26 will set if the engine is running, the PCM detects an improper voltage level on a circuit connected to a QDM for more than 5 seconds.

For QDM "A" to set a Code 26, the brake switch must be closed (brakes not applied). Some QDM circuits will normally switch between high and low. Some scan testers may cause a false Code 26 to set if the engine is running and the service brake is depressed for greater than 30 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

Scheme 185

Scheme 186

1. The PCM does not know which controlled circuit caused code to set. This chart will go through each of the circuits to determine which is at fault. This test checks the SERVICE ENGINE SOON light driver circuit. QDM symptoms include: cooling fan on low speed all the time or won't come on at all, poor driveability due to 100 percent canister purge, improper transaxle shifting and harsh TCC engagement or TCC does not engage.
2. QDM-related codes include Codes 38 and 39. QDM symptoms include: TEMP light on all the time, off during bulb check, cooling fan on low speed all the time or won't come on at all, poor driveability due to 100 percent canister purge and TCC does not engage. (Scheme 185): Code 26 Schematic (3.8L "W" Body) Quad-Driver "A" Error (Scheme 186): Code 26 Flow Chart (3.8L "W" Body) (1 of 4) Quad-Driver "A" Error

CODE 26 - QUAD-DRIVER "A" ERROR (3.8L "W" BODY)(2 OF 4)

Note. Test numbers refer to numbers on diagnostic chart.

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

Monitor voltage at each terminal while wiggling related harness connectors, including PCM harness. If the failure is induced, voltage will change. If no faults are found and code resets for no apparent reason, replace PCM.

Code 26 Flow Chart (3.8L "W" Body) (2 of 4) Quad-Driver "A" Error. Scheme 187

CODE 26 - QUAD-DRIVER "A" ERROR (3.8L "W" BODY)(3 OF 4)

Note. Test numbers refer to numbers on diagnostic chart.

1. 3) This step will determine which circuit is out of specification. If all circuits check out okay, the in-line resistor (used in place of the hot light) and related wiring should be checked. The in-line resistor is taped into the engine harness between the engine electrical center and the PCM pigtails, about 2" from the PCM pigtail junction.

Monitor voltage at each terminal while wiggling related harness connectors, including PCM harness. If the failure is induced, voltage will change. If no faults are found and code resets for no apparent reason, replace PCM.

Code 26 Flow Chart (3.8L "W" Body) (3 of 4) Quad-Driver "A" Error. Scheme 188

CODE 26 - QUAD-DRIVER "A" ERROR (3.8L "W" BODY)(4 OF 4)

Note. Test numbers refer to numbers on diagnostic chart.

1. 4) This test will determine if the problem is the circuit or the component. As the factory installed PCM is protected by an internal circuit breaker, it is unlikely that the PCM needs to be replaced.

Code 26 Flow Chart (3.8L "W" Body) (4 of 4) Quad-Driver "A" Error. Scheme 189

CODE 31 - PARK/NEUTRAL SWITCH CIRCUIT

Note. Complete diagnosis of Code 31 for 3.8L "C", "E" and "H" body vehicles requires GM Tech 1 scan tester, which is capable of indicating status of all 4 park/neutral switch positions. This chart does not apply to 3.8L (VIN L) "C", "E" and "H" body vehicles. Schematics for these models are supplied for reference purposes only.

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 (3.8L) does not exist.
2. Transmission is in high gear.
3. TCC is locked (4T60 transaxle).
4. TPS is less than 15 percent (.94 volt) and vehicle speed is greater than 45 MPH (3T40 transaxle).
5. All above conditions have been met for at least 12 seconds. NOTE: Test numbers refer to numbers on diagnostic chart.

Scheme 190

Scheme 191

Scheme 192

Scheme 193

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. (Scheme 190): Code 31 Schematic (3.8L "C" & "H" Bodies) Park/Neutral Switch Circuit (Scheme 191): Code 31 Schematic (3.8L "E" Body) Park/Neutral Switch Circuit (Scheme 192): Code 31 Schematic (3.8L "W" Body) Park/Neutral Switch Circuit (Scheme 193): Code 31 Flow Chart Park/Neutral Switch Circuit

CODE 34 - MAF SENSOR (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

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.

Harness

Inspect MAF sensor harness to ensure it is not too close to high voltage wires, such as spark plug wires.

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 (3.8L "C" & "H" Bodies) MAF Sensor (Signal Voltage Low). Scheme 194

Code 34 Schematic (3.8L "E" Body) MAF Sensor (Signal Voltage Low). Scheme 195

Code 34 Schematic (3.8L "W" Body) MAF Sensor (Signal Voltage Low). Scheme 196

Code 34 Flow Chart MAF Sensor (Signal Voltage Low). Scheme 197

CODE 35 - IAC IDLE SPEED ERROR WITHOUT 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. NOTE: For IAC reset procedure, see IDLE SPEED & MIXTURE in ADJUSTMENTS article in this section.

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 tester 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 Without Tech 1 (All Models) IAC Idle Speed Error. Scheme 198

Code 35 Flow Chart Without Tech 1 (All Models) IAC Idle Speed Error. Scheme 199

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 Using Tech 1 (All Models) IAC Idle Speed Error. Scheme 200

CODE 36 - SHIFT PROBLEM (3.8L "C" & "H" BODIES)

The 4T60E is an electronically shifted transaxle. Within the transaxle are 4 solenoids for shift and TCC control. Solenoid "A" is energized for 1st through 4th gear operation. Solenoid "B" is energized for 1st gear as well as all 2nd gear operations. The other 2 solenoids are for TCC operation. This trouble code chart deals with shift control solenoids only. When the ignition is turned on, both solenoids "A" and "B" receive battery voltage. The PCM will ground both solenoid drivers for 1st gear until a shift to 2nd gear is commanded. When vehicle speed and TPS reach calibrated values, the PCM will turn off the ground for solenoid "A" and 2nd gear is engaged. Further increase in vehicle speed will cause PCM to turn off the ground for solenoid "B", engaging 3rd gear. When appropriate speed is reached, PCM will again ground solenoid "A" and 4th gear is engaged.

All PRNDL indications are ignored as far as transaxle shifting is concerned except for manual low gear. If the PRNDL inputs indicate manual low has been selected, the PCM will keep both solenoids "A" and "B" energized until about 5400 RPM, when the PCM will force a shift by de-energizing solenoid "A". Manual 2nd and manual 3rd are controlled hydraulically within the transaxle.

Code 36 will not cause the SERVICE ENGINE SOON light to illuminate. When Code 36 is set, the transaxle will be forced into 3rd gear. If code is due to a grounded solenoid "B" driver circuit, only 1st and 2nd gear operation will be available. If code is due to an open in solenoid "B" driver circuit, only 3rd and 4th gear will be available. When the fault goes away, normal operation will be available for the balance of the key cycle.

Code 36 Schematic (3.8L "C" & "H" Bodies) Shift Problem. Scheme 201

Code 36 Flow Chart (3.8L "C" & "H" Bodies) Shift Problem. Scheme 202

CODE 36 - SHIFT PROBLEM (3.8L "E" & "W" BODIES)

4T60E transaxle is electronically shifted. Within transaxle are 4 solenoids. Solenoid "A" is used for 1st and 4th gear operation only. Solenoid "B" is used for 1st and 2nd gear operation. Remaining 2 solenoids are for TCC operation only. All PRNDL indications are ignored as far as transaxle shifting is concerned except manual low.

Code 36 will set if solenoid "B" failed in OFF position, which will cause transaxle to be in 3rd gear, and desired gear is 1st, TPS is greater than 5 percent, VSS is greater than 5 MPH and Codes 21, 22 and 24 are not present. Code will also set if solenoid "B" failed in ON position, which will cause transaxle to be in 1st gear, and desired gear is 4th, PRNDL is in 3rd or 4th, TPS is greater than 10 percent and Codes 31, 21 and 22 are not present.

When Code 36 is set, transaxle will be forced into 3rd gear. If code sets due to a grounded circuit No. 1223, only 1st and 2nd gear operation will be available. If circuit No. 1223 is open, only 3rd and 4th gear operation will be available. If fault goes away, normal operation will be resumed for duration of key cycle.

Code 36 Schematic (3.8L "E" Body) Shift Problem. Scheme 203

Code 36 Schematic (3.8L "W" Body) Shift Problem. Scheme 204

Code 36 Flow Chart (3.8L "E" & "W" Bodies) Shift Problem. Scheme 205

CODE 38 - BRAKE SWITCH

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

Scheme 206

Scheme 207

Scheme 208

Scheme 209

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. (Scheme 206): Code 38 Schematic (3.8L "C" & "H" Bodies) Brake Switch (Scheme 207): Code 38 Schematic (3.8L "E" Body) Brake Switch (Scheme 208): Code 38 Schematic (3.8L "W" Body) Brake Switch (Scheme 209): Code 38 Flow Chart Brake Switch

CODE 39 - TCC CIRCUIT W/O TECH 1 (3.8L W/4T60 TRANS)

Code 39 will set when Codes 28 and 29 are not set, brake is not applied, TCC is commanded by ECM, transaxle 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

Scheme 210

Scheme 211

Scheme 212

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. (Scheme 210): Code 39 Schematic W/O Tech 1 (3.8L "C & H" Body W/4T60) TCC Circuit (Scheme 211): Code 39 Schematic W/O Tech 1 (3.8L "W" Body W/4T60) TCC Circuit (Scheme 212): Code 39 Flow Chart W/O Tech 1 (3.8L W/4T60 Trans.) TCC Circuit

CODE 39 - TCC CIRCUIT USING TECH 1 (3.8L W/4T60 TRANS)

Code 39 will set when Codes 28 and 29 are not set, brake is not applied, TCC is commanded by ECM, transaxle 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

Scheme 213

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. see scheme 67: Code 39 Schematic Using Tech 1 (3.8L "C & H" Body W/4T60) TCC Circuit see scheme 68: Code 39 Schematic Using Tech 1 (3.8L "W" Body W/4T60) TCC Circuit (Scheme 213): Code 39 Flow Chart Using Tech 1 (3.8L W/4T60 Trans.) TCC Circuit

CODE 41 - CAM SENSOR CIRCUIT (3.8L "C", "E" & "H" BODIES)

Code 41 will set if engine is running and a cam sensor signal is not received by ECM for last 2-5 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. Verifies proper operation of circuits No. 633, 644 and 645.
2. Tests cam signal circuit from C(3)I ignition module to ECM.
3. If harmonic balancer windows are interfacing with cam sensor, voltage reading may be zero. Bumping engine using starter will cause condition to go away.
4. If voltage reading is varying around a midpoint of 10.5 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

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.

If connections and harness are okay, connect a digital volt-ohmmeter (10-megohm) between ground and circuit No. 630 terminal at ECM. Monitor DVOM while moving related connectors and wiring harness. Voltage reading will change if failure is induced. This may help isolate malfunction.

Code 41. Scheme 214

CODE 41 - CAM SENSOR CIRCUIT (TYPE II, "C", "E", "H" & "W" BODY)

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

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 (10-megohm) between ECM cam signal terminal 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 Flow Chart (Type II Coil) Cam Sensor Circuit. Scheme 215

CODE 42 - EST CIRCUIT OPEN OR GROUNDED

Note. For circuit reference, use accompanying schematic(s).

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 energized by 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, circuit No. 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 Circuit Open Or Grounded. Scheme 216

CODE 43 - ESC ERROR (WITHOUT 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 W/O ESC Module (All Models) ESC Error. Scheme 217

Code 43 Flow Chart W/O ESC Module (All Models) ESC Error. Scheme 218

CODE 44 - LEAN EXHAUST INDICATION

O2 sensor acts like an open 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 44 will reflect a lean left O2 sensor; Code 64 will indicate a lean right O2 sensor. Perform test procedures for right or left sensor as necessary.

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 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 44 Flow Chart (All Models) Lean Exhaust Indication. Scheme 219

CODE 45 - RICH EXHAUST INDICATION

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 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 45 Flow Chart (All Models) Rich Exhaust Indication. Scheme 220

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 221

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.

CODES 53, 54 & 55 - EGR FAULT (3.8L (VIN L) EXCEPT "E" BODY)

Codes 53, 54 and 55 are EGR flow test failures. PCM tests medium and large EGR solenoid valves by cycling each of them on momentarily while monitoring engine RPM. When a solenoid is turned on, PCM expects to see a drop in engine RPM. If expected drop is not detected for EGR solenoid No. 1 for 8 out of 12 tests, Code 53 will set. If expected drop is not detected for medium EGR solenoid (EGR No. 2) for 6 out of 8 tests, Code 54 will set. If expected drop is not detected for large EGR solenoid (EGR No. 3) for 3 out of 5 times, Code 55 will set.

PCM runs EGR flow tests when coolant temperature is greater than 183°F (84°C), vehicle is in a coast-down mode (but not in a fuel-cut situation), O2 sensor voltage is greater than .57 volt, transmission is in 1st or 2nd gear, A/C clutch is not engaged, and vehicle speed is greater than 25 MPH. EGR No. 1 engine test speed range is 800-1000 RPM. EGR No. 2 engine test speed range is 825-1025 RPM. EGR No. 3 engine test speed range is 850-1050 RPM.

Note. Test numbers refer to numbers on diagnostic chart.

1. A noticeable change in engine speed should occur as each solenoid is cycled on at idle.
2. If test light glows, PCM and wiring are okay.

Check for poor harness connections or harness damage. If no problems are found, turn ignition on. Backprobe applicable PCM terminals with a DVOM while wiggling harness. If a failure is induced, voltage reading will change. If no problems are found, check EGR valve pintles and orifices for excessive carbon build-up. Also, check for plugged EGR tube or passages.

Code 53, 54 & 55 Schematic (3.8L (VIN L) "C" & "H" Body) EGR Fault. Scheme 222

Code 53, 54 & 55 Schematic (3.8L "W" Body) EGR Fault. Scheme 223

Code 53, 54 & 55 Flow Chart (3.8L (VIN L) Except "E" Body) EGR Fault. Scheme 224

CODES 54 & 55 - EGR FAULT (3.8L (VIN 1) "C" & "H" BODIES)

Codes 54 and 55 are EGR flow test failures. PCM tests medium and large EGR solenoid valves by cycling each of them on momentarily while monitoring engine RPM. When a solenoid is turned on, PCM expects to see a drop in engine RPM. If expected drop is not detected for medium EGR solenoid (EGR No. 2) for 6 out of 8 tests, Code 54 will set. If expected drop is not detected for large EGR solenoid (EGR No. 3) for 3 out of 5 times, Code 55 will set.

PCM runs EGR flow tests when coolant temperature is greater than 160°F (71°C), vehicle is in a coast-down mode (but not in a fuel-cut situation), O2 sensor voltage is greater than .6 volt, transmission is in 1st or 2nd gear and vehicle speed is greater than 5 MPH. EGR No. 2 engine test speed range is 850-1200 RPM. EGR No. 3 engine test speed range is 900-1400 RPM.

Note. Test numbers refer to numbers on diagnostic chart.

1. A noticeable change in engine speed should occur as each solenoid is cycled on at idle.
2. If test light glows, PCM and wiring are okay.

Check for poor harness connections or harness damage. If no problems are found, turn ignition on. Backprobe applicable PCM terminals with a DVOM while wiggling harness. If a failure is induced, voltage reading will change. If no problems are found, check for check EGR valve pintles and orifices for excessive carbon build-up. Also, check for plugged EGR tube or passages.

Code 54 & 55 Schematic (3.8L (VIN 1) "C" & "H" Bodies) EGR Fault. Scheme 225

Code 54 & 55 Flow Chart (3.8L (VIN 1) "C" & "H" Bodies) EGR Fault. Scheme 226

CODE 55 - ECM ERROR (EXCEPT 3.8L (VIN 1))

Ensure correct MEM-CAL or PROM is being used and that it is properly installed. If so, replace control module. Clear codes, confirm closed loop operation and check operation of SERVICE ENGINE SOON light.

CODE 56 - QUAD-DRIVER ERROR (3.8L EXCEPT "E" BODY)(1 OF 2)

ECM uses Quad-Driver Modules (QDMs) to control several devices. When ECM is commanding a component on, voltage of output circuit will be low (near zero volts). When ECM is commanding component off, voltage of output circuit will be high (near battery voltage). Primary function of quad-driver module is to control ground circuit for component being controlled. ECM has an internal fault line for each quad-driver module. Fault line status can be displayed on a scan tester. If ECM detects an output voltage other than what is expected on fault line, ECM will set Code 56.

Note. Test numbers refer to numbers on diagnostic chart.

1. PCM does not know which controlled circuit caused Code 56 to set. This chart will check each circuit to determine which is at fault. If other QDM-related codes are present, use those charts first.
2. If QDM "B" related symptoms are present, checks on Code 56 (2 of 2) chart should isolate cause of fault.
3. These steps help determine which circuit is out of specification.

Quad-Driver Related Symptoms

1. Improper shifting.
2. TCC will not apply or harsh engagement.
3. Poor driveability due to constant EGR.

Monitor voltage at each terminal shown in schematic while moving related harness connectors, including PCM harness. If failure is induced, voltage will change. This may help to isolate an intermittent condition. Check for bent pins at PCM. If code reoccurs with no apparent connection problem, replace PCM.

Code 56 Schematic (3.8L (VIN L) "C" & "H" Bodies) Quad-Driver Error. Scheme 227

Code 56 Schematic (3.8L (VIN 1) "C" & "H" Bodies) Quad-Driver Error. Scheme 228

Code 56 Schematic (3.8L "W" Bodies) Quad-Driver Error. Scheme 229

Code 56 Flow Chart (3.8L Except "E" Body)(1 Of 2) Quad-Driver Error. Scheme 230

CODE 56 - QUAD-DRIVER ERROR (3.8L EXCEPT "E" BODY)(2 OF 2)

ECM uses Quad-Driver Modules (QDMs) to control several devices. When ECM is commanding a component on, voltage of output circuit will be low (near zero volts). When ECM is commanding component off, voltage of output circuit will be high (near battery voltage). Primary function of quad-driver module is to control ground circuit for component being controlled. ECM has an internal fault line for each quad-driver module. Fault line status can be displayed on a scan tester. If ECM detects an output voltage other than what is expected on fault line, ECM will set Code 56.

Note. Test number refers to number on diagnostic chart.

Scheme 231

1. 4) This step helps determine if problem is circuit or component. (Scheme 231): Code 56 Flow Chart (3.8L Except "E" Body)(2 Of 2) Quad-Driver Error

CODE 57 - BOOST CONTROL PROBLEM (3.8L (VIN 1))

Under most conditions, PCM commands boost control solenoid to operate at a 100 percent duty cycle (on) to allow full boost upon demand; however, if reverse gear is selected, PCM detects rapid deceleration, or if engine load is extremely high, reduced boost pressure is desired. Under these conditions, PCM commands boost control solenoid to operate at zero percent duty cycle (off), which opens by-pass valve to reduce boost pressure by recirculating it back through supercharger inlet. If PCM detects a malfunction in boost control system that causes engine torque to be too high (by-pass valve not opening), it will illuminate SERVICE ENGINE SOON light and set Code 57.

Note. Test numbers refer to numbers on diagnostic chart.

Scheme 232

Scheme 233

1. If boost control driver circuit becomes shorted to ground between solenoid and PCM, by-pass valve will remain closed when PCM attempts to command it open. This could cause an overboost condition during high engine load situations.
2. No inlet vacuum to by-pass valve actuator may cause by-pass valve to remain closed during deceleration. This condition will be perceived as a sail-on condition, possibly accompanied by a rough idle.
3. This step checks for a sticking boost control solenoid. (Scheme 232): Code 57 Schematic (3.8L (VIN 1) "C" & "H" Bodies) Boost Control Problem (Scheme 233): Code 57 Flow Chart (3.8L (VIN 1) "C" & "H" Bodies) Boost Control Problem

CODE 58 - PASS-KEY FUEL ENABLE CIRCUIT (3.8L EXCEPT "W" BODY)

Personal Automotive Security System (PASS-Key) is designed to disable vehicle operation if an incorrect ignition key or starting procedure is used. If correct key and starting technique are used, PASS-Key decoder module sends a fuel enable signal to PCM and energizes starter enable relay. If proper signal does not reach PCM on fuel enable input line, PCM will not pulse injectors and vehicle will not start; Code 58 will set.

Note. Test numbers refer to numbers on diagnostic chart.

1. If vehicle will not crank with Code 58 stored, problem affects entire PASS-KEY system and is not isolated to fuel enable circuit.
2. PCM applies and monitors a 5-volt signal on circuit No. 229. Decoder module will pulse this signal to ground when proper key and starting technique are used. This test ensures PCM is supplying 5-volt signal and circuit is not open or shorted to ground.
3. Checks PWM signal from PASS-KEY module. Because 5 volts supplied by PCM is being pulsed to ground, voltage on circuit No. 229 should measure about 2.5 volts.
4. Checks for faulty PCM or intermittent condition by clearing codes. Because PCM ignores absence of fuel enable signal only when Code 58 is stored, vehicle should not start if problem is present and Code 58 is not.

Pass-Key Diagnosis

PASS-Key is a sophisticated system which interfaces PASS-Key decoder module, PCM and starter with a power source, starter enable relay, ignition switch, instrument cluster and Remote Accessory Control (RAC) module.

Note. Testing and servicing PASS-Key decoder module requires special test equipment and documentation.

Before replacing decoder module, check system for following common problems

Scheme 234

Scheme 235

Scheme 236

1. Check ignition key pellet sensing contacts in ignition lock cylinder. Look into cylinder lock. If contacts are damaged, replace cylinder lock.
2. Check fuse No. 11 in instrument panel fuse block.
3. Check fuse No. 4 in right underhood fuse block.
4. Check fuse No. 8 in relay center.
5. Check security indicator bulb in instrument panel.
6. A defective resistor pellet within ignition key or incorrect resistance value of key (15 different assigned values) will prevent vehicle from starting. Key must be correct electrically and mechanically. If incorrect key is used to try to start vehicle, decoder will not allow vehicle to start for 2-4 minutes, even after correct key is inserted. (Scheme 234): Code 58 Schematic (3.8L "C" & "H" Bodies) Pass-Key Fuel Enable Circuit (Scheme 235): Code 58 Schematic (3.8L "E" Body) Pass-Key Fuel Enable Circuit (Scheme 236): Code 58 Flow Chart (3.8L Except "W" Body) Pass-Key Fuel Enable Circuit

CODE 61 - CRUISE VENT SOLENOID (3.8L)

Cruise switch within turn signal lever receives ignition voltage from a 15-amp fuse on circuit No. 639. Cruise switches are inputs to cruise control portion of PCM. Cruise servo and vent and vacuum solenoids are output lines and are controlled by high side drivers in PCM. With ignition on, PCM looks at these output lines and will set a code depending upon actual status of these lines compared with commanded status. In this manner, PCM can detect opens or shorts to ground or voltage.

Code 61 Schematic (3.8L "C" & "H" Bodies) Cruise Vent Solenoid. Scheme 237

Code 61 Schematic (3.8L "E" Body) Cruise Vent Solenoid. Scheme 238

Code 61 Schematic (3.8L "W" Body) Cruise Vent Solenoid. Scheme 239

Code 61 Flow Chart (3.8L) Cruise Vent Solenoid. Scheme 240

CODE 62 - CRUISE VACUUM SOLENOID (3.8L)

Cruise switch within turn signal lever receives ignition voltage from a 15-amp fuse on circuit No. 639. Cruise switches are inputs to cruise control portion of PCM. Cruise servo, vent and vacuum solenoids are output lines and are controlled by high side drivers in PCM. With ignition on, PCM looks at these output lines and will set a code depending upon actual status of these lines compared with commanded status. In this manner, PCM can detect opens or shorts to ground or voltage.

Code 62 Flow Chart (3.8L) Cruise Vacuum Solenoid. Scheme 241

CODE 63 - CRUISE SYSTEM PROBLEM (3.8L EXCEPT "E" BODY)

The PCM-controlled cruise control system is designed to monitor itself to ensure the desired cruise position and actual cruise position are equal to each other. If actual servo position is too low when maximum servo position is commanded, Code 63 will set. Code will set if throttle angle is less than 50 percent, desired servo position is 90 percent, actual servo position is less than 2 percent and all conditions have been met for at least 3 seconds. Code 63 will not turn on the SERVICE ENGINE SOON light.

A cruise control throttle cable which binds or intermittently sticks can cause a Code 63 to set. Outside electrical interference (such as a CB antenna lead near the PCM wiring harness) may induce a false servo position signal and set Code 63.

Code 63 Flow Chart (3.8L Except "E" Body) Cruise System Problem. Scheme 242

CODE 65 - CRUISE SERVO POSITION (3.8L)

PCM supplies 5 volts to cruise control servo position sensor. Depending upon actual servo position, voltage on servo position sensor circuit will indicate to PCM position of servo. Code 65 will set if circuit No. 399 is open or if circuit No. 398 is open or shorted to ground or voltage.

Code 65 Flow Chart (3.8L) Cruise Servo Position. Scheme 243

CODE 66 - LOW A/C REFRIGERANT CHARGE (3.8L EXCEPT "E" BODY (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.

Scheme 244

Scheme 245

Scheme 246

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. (Scheme 244): Code 66 Schematic (3.8L "C" & "H" Bodies W/O Digital Display) Low A/C Refrigerant Charge (Scheme 245): Code 66 Schematic (3.8L "W" Body W/O Digital Display) Low A/C Refrigerant Charge (Scheme 246): Code 66 Flow Chart (3.8L Except "E" Body (W/O Digital Display)) Low A/C Refrigerant Charge

CODE 66 - LOW A/C REFRIGERANT CHARGE (3.8L "C" & "H" BODIES (W/DIGITAL DISPLAY))

PCM 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, PCM 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.

Scheme 247

Scheme 248

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. (Scheme 247): Code 66 Schematic (3.8L "C" & "H" Bodies W/Digital Display) Low A/C Refrigerant Charge (Scheme 248): Code 66 Flow Chart (3.8L "C" & "H" Bodies W/Digital Display) Low A/C Refrigerant Charge

CODE 67 - CRUISE ENGAGE SWITCHES (3.8L EXCEPT "W" BODY)

Code 67 will set if circuit No. 397 or 86 is open, set/coast or resume/accel switch is closed for an extended amount of time or any cruise engage switch circuit is shorted to voltage.

Code 67 Schematic ("C" & "H" Bodies) Cruise Engage Switches. Scheme 249

Code 67 Schematic ("E" Body) Cruise Engage Switches. Scheme 250

Code 67 Flow Chart (Except "W" Body) Cruise Engage Switches. Scheme 251

CODE 67 - CRUISE SWITCHES (3.8L (VIN L) "W" BODY)

Code 67 will set if the cruise "on/off" signal circuit is open, if set/coast or resume/accel switch signal is present for greater than 7 1/2 seconds, indicating a switch problem, or if brake switch status has not changed after 5 stops from greater than 35 MPH. Code will also set if any of the cruise circuits become shorted to voltage. Code 67 will set if any one of the described conditions occur; however, the SERVICE ENGINE SOON light will not illuminate. A short to ground in the cruise engage switch circuits will cause the switch to fail but will not blow the 15-amp fuse for the power supply circuit.

Code 67 Schematic (3.8L "W" Body) Cruise Switches. Scheme 252

Code 67 Flow Chart (3.8L "W" Body) Cruise Switches. Scheme 253

CODE 68 - CRUISE SYSTEM PROBLEM (USING TECH 1) (3.8L)

PCM-integrated cruise control system is designed to monitor itself to ensure desired cruise position and actual cruise position are equal to each other. Code 68 sets when actual servo position sensor signal is 12 percent greater than desired servo position sensor signal for 1.5 seconds.

Outside interference such as CB antenna lead near PCM wiring harness may cause false servo position sensor signal and set Code 68.

Code 68 Flow Chart Using Tech 1 (3.8L) Cruise System Problem. Scheme 254

CODE 69 - A/C HEAD PRESSURE SWITCH (3.8L "C" & "H" BODIES)

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 (3.8L "C" & "H" Bodies) A/C Head Pressure Switch. Scheme 255

Code 69 Flow Chart (3.8L "C" & "H" Bodies) A/C Head Pressure Switch. Scheme 256

CODE 69 - A/C HEAD PRESSURE SWITCH (3.8L "W" BODY)

A/C head pressure switch opens at 200 psi (13.8 kg/cm 2 ). When switch is open, 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 (3.8L "W" Body) A/C Head Pressure Switch. Scheme 257

Code 69 Flow Chart (3.8L "W" Body) A/C Head Pressure Switch. Scheme 258

CODE 85 - PROM ERROR & CODE 87 - EEPROM ERROR

Ensure all ECM connectors are fully inserted in socket. If okay, have ECM reprogrammed using appropriate equipment. If equipment is not available, have ECM serviced through dealership.

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:
• SELF-DIAGNOSTIC SYSTEM
• RETRIEVING CODES (NON-SCAN)
• HARD OR INTERMITTENT TROUBLE CODE DETERMINATION
• SCAN TESTER USAGE
• SCAN DATA
• CLEARING TROUBLE CODES
• TEMPERATURE-TO-RESISTANCE VALUES