Engine Controls - Tests W/codes - 3.1L: Other Oldsmobile Achieva I

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.

RETRIEVING CODES (NON-SCAN)

Note. On models using a 12-terminal DLC (previously referred to as the ALDL), if a wire is present at terminal "B", inserting a jumper wire into test and ground terminals of DLC 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 the ENGINE PERFORMANCE section. On models not using a 12-terminal DLC or not having a wire present in terminal "B", codes must be retrieved using a hand-held scan tester.

DATA LINK CONNECTOR (DLC) TEST TERMINALS

1. Turn ignition on. DO NOT start engine. SERVICE ENGINE SOON light should glow. Locate DLC attached to control module wiring harness. Most DLC's are located under dash on driver side of vehicle. For exact location of DLC, see COMPONENT LOCATIONS in the «SYSTEM/COMPONENT TESTS - 3.1L»(ref-19615) article in this section. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of DLC. (Scheme 47)
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»(ref-19653) article in this section. To exit diagnostic mode, turn ignition off and remove jumper wire from DLC connector.

Scheme 47

Field Service Mode Check (If Available)

If DLC 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. Some models require the use of a scan tester to enter field service mode. Field service mode check can be found by proceeding to FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.

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 the 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 DLC, 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.

Vehicles utilizing a 16-terminal DLC or 12-terminal DLC with terminal "B" not used, must use a scan tester for retrieving codes or enter Field Service Mode.

Note. Code 12 should always exist when DLC terminal "B" 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 calibration will not set a trouble code but will cause driveability problems.

Using a scan tester is the 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 DLC 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 a minimum of 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.

MULTIPORT FUEL INJECTION (MFI)

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 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.

CODE 14, COOLANT TEMPERATURE SENSOR SIGNAL VOLTAGE LOW

1. For shared sensor ground tie-offs, see appropriate diagram in «WIRING DIAGRAMS»(ref-19583-S27559351752001031200000) section. NOTE: This chart assumes engine cooling system is functioning properly (not overheating). Test numbers refer to numbers on diagnostic chart.

1. Code 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 still exist.
2. This tests for grounded sensor signal line between control module and coolant sensor.

CODE 15, COOLANT TEMPERATURE SENSOR SIGNAL VOLTAGE HIGH

1. For shared sensor ground tie-offs, see appropriate diagram in «WIRING DIAGRAMS»(ref-19583-S27559351752001031200000) section. NOTE: Test numbers refer to numbers on diagnostic chart.

1. Code 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 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.

CODE 17, CAMSHAFT SENSOR ERROR

Camshaft sensor is a Hall Effect switch located on the front of the engine. Sensor sends signals to the PCM when cylinder No. 1 is on the intake stroke. Signal is used by PCM to synchronize sequential fuel injection. If cam signal is not received by PCM, PCM will pulse fuel injectors sequentially, but the fuel injectors may not be in sync with each intake valve opening. A loss of this signal, or any extra signals (false signals), at engine speeds greater than 500 RPM will cause PCM to set a Code 17.

Note. Test numbers refer to numbers on diagnostic chart.

1. PCM performs a test for Code 17 when the engine is running or cranking. Code 17 will set when a cam pulse is missing on the first pass through the internal PCM self-test of the camshaft position sensor, or a cam pulse is missing for 3 seconds.
2. By repeatedly tapping the starter, camshaft timing mark and camshaft position sensor will align with each other. At this point, voltage from sensor to PCM should drop to near zero volts temporarily. This indicates the camshaft sensor is capable of sending a signal to the PCM.
3. Before replacing camshaft position sensor, inspect sensor for proper installation.

CODE 21, THROTTLE POSITION SENSOR SIGNAL VOLTAGE HIGH

1. For shared sensor ground tie-offs, see appropriate diagram in «WIRING DIAGRAMS»(ref-19583-S27559351752001031200000) section. 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.

CODE 22, THROTTLE POSITION SENSOR SIGNAL VOLTAGE LOW

1. For shared sensor ground tie-offs, see appropriate diagram in «WIRING DIAGRAMS»(ref-19583-S27559351752001031200000) section. 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 setting code. 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.

CODE 24, VEHICLE SPEED SENSOR

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 2 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 2 MPH.
2. Before replacing control module, PROM/MEM-CAL should be checked for correct application.

CODE 28, TRANSMISSION RANGE PRESSURE SWITCH

Transmission range switch is part of Transmission Neutral Start Switch (TMNSS) mounted on transaxle assembly. Transmission range switch is a multi-signal switch that sends information, relative to gear selector position, to PCM. PRNDL input consists of 4 discrete circuits to pull 4 PCM voltages low in various combinations to indicate each gear range. Voltage level of each of the circuits is represented as low equals grounded circuit and high equals open circuit. The 4 states displayed represent decoder parity, "A", "B"and "C" respectively.

Code P0705 will set when the following conditions are present.

1. Ignition is on and engine off.
2. Vehicle speed is zero MPH.
3. PRNDL inputs indicate a gear other than Park and Neutral.
4. All conditions are met for .13 second for 3 consecutive start-ups.

Or

1. PRNDL inputs status indicators ("P", "A", "B"and "C") indicate an incorrect combination of low and high for a minimum of 10 seconds. PCM will also command stepper motor cruise control to be inhibited.

Code P0705 will cause PCM to command a drive-4 shift position. Code P0705 does not illuminate the Malfunction Indicator Light (MIL).

Note. Test numbers refer to numbers on diagnostic chart.

1. 1) & 2) This step checks for proper operation of transmission range switch.
2. 3) This test checks for an open or grounded circuit. When Code P0705 is present, PCM assumes drive-4 position until a correct combination is received by PCM. Some gear select positions may not be possible until fault is repaired.

CODE 33, MAP SENSOR SIGNAL VOLTAGE HIGH

1. For shared sensor reference and shared sensor ground tie -offs, see appropriate diagram in «WIRING DIAGRAMS»(ref-19583-S27559351752001031200000) section. NOTE: Test numbers refer to numbers on diagnostic chart.

1. This test confirms Code 33 and determines if it is result of a hard failure or an intermittent condition. Code 33 will set when voltage signal reading is too high for greater than a precalibrated period of time, TPS voltage indicates throttle is closed and neither Code 21 nor 22 is present.
2. This step simulates conditions for a Code 34. If control module recognizes and sets Code 34, low MAP signal, control module and 5-volt reference and MAP signal circuits are not at fault. If ground circuit is shared with other sensors and ground circuit becomes open, additional codes related to these sensors may be set.

CODE 35, IAC IDLE SPEED ERROR

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.

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 (3.1L) IAC Idle Speed Error. Scheme 48

Code 35 Flow Chart (3.1L) IAC Idle Speed Error. Scheme 49

CODE 36, 24X SIGNAL ERROR

The 24X crankshaft position sensor is used to improve spark during low engine speeds. Code 36 will set if the engine is running and the PCM detects 6 or more 24X crankshaft sensor reference pulses have not occurred. Code 36 diagnosis occurs once per ignition cycle.

Note. Test numbers refer to numbers on diagnostic chart.

1. The 24X signal RPM should be the same as engine speed up to 2000 RPM, at which time it stops. This test determines if the PCM is putting out a 24X signal.
2. Determines if signal voltage is present at the PCM.
3. Determines is battery voltage is present at sensor input.
4. Applying battery voltage to the 24X pigtail circuit determines pigtail and sensor integrity.
5. Determines ground path continuity.

CODE 37, TCC BRAKE SWITCH ERROR

PCM monitors activity of the normally-closed brake switch. Switch opens when brake pedal is applied.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for voltage at brake switch.
2. Simulates brake switch closed or brakes off.
3. Checks TCC brake switch circuit between PCM and switch.

CODE 41, CYLINDER SELECT ERROR

Ignition timing is controlled by the PCM. Inputs from various sensors allow PCM to calculate optimum spark timing.

Note. Test number refers to number on diagnostic chart.

1. Confirms Code 41 and fault causing code is present.
2. Checks for normal IC ground path through ignition module

CODE 42, IC CIRCUIT OPEN/GROUNDED

Code 42 indicates PCM has seen an open or short to ground in HEI EST or by-pass circuit.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test confirms Code 42 and determines if fault is a hard failure or intermittent condition.
2. This test checks for a normal IC ground path through ignition module. If EST circuit is shorted to ground, reading will be less than 500 ohms.
3. As test light voltage touches by-pass circuit, module should switch. This will cause ohmmeter to switch from hundreds of ohms to thousands of ohms. This test assures module "switched".
4. If module did not switch, this tests for a short in IC circuit, an open in by-pass circuit and a faulty ignition module connection or module.
5. This step confirms Code 42 is a faulty PCM and not an intermittent problem in IC or by-pass Circuits.

CODE 43, ESC ERROR

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. PCM 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.

CODE 44, LEAN EXHAUST INDICATION

Note. Some models engines are equipped with 2 oxygen sensors. On these models, Code 44 will set if the left sensor circuit is lean. Code 64 will set if the right sensor circuit is lean. Use this chart for Code 64 also and perform tests for applicable sensor.

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. On models with 2 oxygen sensors, 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".

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 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 44 Flow Chart (3.1L) Lean Exhaust Indication. Scheme 50

Code 44 Flow Chart. Scheme 51

CODE 45, RICH EXHAUST INDICATION

Note. On some models engines are equipped with 2 oxygen sensors. On these models, Code 45 will set if the left sensor circuit is rich. Code 65 will set if the right sensor circuit is lean. Use this chart for Code 65 also and perform tests for applicable sensor.

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.

On models using 2 oxygen sensors, Code 45 will reflect a rich left O2 sensor; Code 65 will indicate a rich right O2 sensor. Perform test procedures for right or left sensor as necessary.

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.

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 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 45 Flow Chart (3.1L) Rich Exhaust Indication. Scheme 52

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 54, FUEL PUMP VOLTAGE LOW

Fuel pump circuit No. 120 is monitored and used by PCM for fuel system compensations based on system voltage. Signal is also used to store a trouble code if fuel pump relay is defective or fuel pump voltage is lost while engine is running. About 12 volts should exist on fuel pump signal circuit for 2 seconds after ignition is turned on or any time reference pulses are being received by PCM.

Code 54 will set if voltage on circuit is greater than 14 volts or less than 7 volts for 3 second.The oil pressure switch will provide a current path for fuel pump when oil pressure becomes great enough to close the contacts. Malfunction Indicator Light (MIL) will illuminate.

Code 54 Schematic (3.1L) Fuel Pump Voltage Low. Scheme 53

Code 54 Flow Chart (3.1L) Fuel Pump Voltage Low. Scheme 54

CODE 55, PCM ERROR

Ensure PCM grounds are okay. Ensure correct EPROM is being used and that it is properly installed. If okay, replace PCM. Clear codes, confirm closed loop operation and check operation of Malfunction Indicator Light (MIL).

CODE 58, TRANSMISSION TEMPERATURE SENSOR HIGH TEMPERATURE

Temperature sensor is a 2 wire thermistor located in transaxle. This sensor operates in the same manner as engine coolant temperature sensor and intake air temperature sensor. PCM applies 5 volts to sensor on signal circuit. Voltage sensed at PCM signal circuit terminal will be high when trans fluid is cold and as fluid warms voltage signal will drop. A very low signal voltage indicates a high fluid temperature or a failure in sensor circuit. Normal fluid temperature range is between 167°F-212°F (75°C-100°C).

Code 58 will set when sensor indicates a temperature of 148°C or greater for 5 seconds. Malfunction Indicator Light (MIL) will illuminate and PCM will use a default sensor value of 90°C.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for a short to ground or an out-of-calibration sensor.
2. Checks for an internal fault within the transmission by creating an open.

CODE 59, TRANSMISSION TEMPERATURE SENSOR LOW TEMPERATURE

Temperature sensor is a 2 wire thermistor located in transaxle. This sensor operates in the same manner as engine coolant temperature sensor and intake air temperature sensor. PCM applies 5 volts to sensor on signal circuit. Voltage sensed at PCM signal circuit terminal will be high when trans fluid is cold and as fluid warms voltage signal will drop. A very high signal voltage indicates a low fluid temperature or a failure in sensor circuit. Normal fluid temperature range is between 167°F-212°F (75°C-100°C).

Code 59 will set when sensor indicates a temperature of less than -40°C for 5 seconds. Malfunction Indicator Light (MIL) will not illuminate and PCM will use a default sensor value of 90°C.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test determines if a current condition exists.
2. Simulates a Code 58. If PCM recognizes low signal voltage, and scan displays 146 degrees centigrade or higher, PCM and wiring are okay.
3. Checks if signal circuit is open. Five volts should be present at sensor connector.

CODE 70, HIGH A/C PRESSURE

A/C pressure sensor responds to changes in A/C refrigerant system high side pressure. PCM uses A/C compressor load input to determine engine idle speed. Sensor uses a 5-volt reference signal from PCM and returns an input signal to PCM on a separate line. Low pressure (zero psi) will return a signal of about .1 volt. High pressure will return a signal of about 4.9 volts. ECM will disable A/C if Code 66 is present.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks the voltage signal being received by the PCM from the A/C refrigerant pressure sensor.
2. Checks to see if the high voltage signal is from a shorted sensor or a short to voltage in the circuit. Normally, disconnecting the sensor would make a normal circuit go to near zero volts.

CODE 72, VSS

Speed sensor is a PM generator located on transmission output shaft.

Note. Test numbers refer to numbers on diagnostic chart.

1. Disable TC system (if equipped) when performing this step. Whenever ignition is cycled off and then back on, TC system will default on.
2. An intermittent connection at VSS or PCM may cause code to set. Inspect harness and all related connections. Check for damage or pushed out terminals. Prior to replacing PCM check for updated software for PCM (reprogrammable).
3. Ensure harness is not routed too close to hot exhaust components.

CODE 75, 76 OR 77, EGR SOLENOID ERROR

The PCM performs an EGR diagnostic check to monitor the flow of exhaust gases through the 3 EGR solenoids. When the vehicle is under deceleration, the EGR valves are normally closed. The PCM then opens each valve in succession (while keeping previous valves open) and manifold vacuum is monitored for a calculated MAP increase associated with each valve's application. Should the expected response of manifold vacuum not be seen by the PCM, a Code 75 (solenoid No.1), 76 (solenoid No. 2) or 77 (solenoid No. 3) will set.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test determines if there is power to the EGR valve.
2. This test will determine if there is an open circuit in the EGR wiring or if the EGR valve is at fault.
3. This test will determine if there is a short to ground in the solenoid drive circuits or if the PCM is at fault.

CODE 80/90, TRANSAXLE COMPONENT SLIPPING

PCM monitors difference between engine speed and transaxle input shaft speed. With selector in D3 or D4 (indicated gear 3 or 4), and TCC is locked, scan should display engine speed closely matching input speed.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for a shorted internal transaxle harness or TCC solenoid.
2. Checks for open in power supply to TCC solenoid.

CODE 82, 3X SIGNAL ERROR

If scan tester did not indicate a cranking RPM, and there is no spark present at the plugs, the problem lies in the electronic ignition system or the power and ground supplies to the module. The magnetic crank sensor is used to determine engine crankshaft position much the same way as the pick-up coil did in the distributor type system. The sensor is mounted in the block near a 7-slot wheel on the crankshaft.

The rotation of the wheel creates a magnetic field in the sensor which induces a voltage signal. The electronic ignition module then processes this signal and creates the reference pulses needed by the PCM and the signal triggers the correct coil at the correct time.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test will determine if the 12-volt supply and a good ground are available at the ignition module.
2. Checks for resistance of the crank sensor and connections.
3. Voltage will vary in this test depending on cranking speed of engine.

CODE 85, PROM ERROR & CODE 87, EEPROM ERROR

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

CODE 86, ANALOG/DIGITAL ERROR

If any other codes are present, use those charts first. The Analog/Digital (A/D) multiplexer chip is an internal part of the PCM. Some PCM sensor inputs lead to the A/D multiplexer. If any one of them shorts to battery voltage for more than 15 seconds, the A/D error diagnostic code will set, resulting in a Code 86.

CODE 96, TRANSMISSION VOLTAGE LOW

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for normal battery voltage of 9-15 volts.
2. Checks if low voltage is due to generator voltage supply circuit, or PCM. If voltage is less than 9 volts, PCM is okay.

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.

3.1L (VIN M) PCM Wiring Diagram (1 Of 2). Scheme 55

3.1L (VIN M) PCM Wiring Diagram (2 Of 2). Scheme 56