2.8l VIN [w] Pfi Cec Tests W/codes Oldsmobile Cutlass Ciera I

MODEL IDENTIFICATION

Repair procedures in this article are sometimes identified by a specific body code. The following table lists GM division, model name, and body types that apply to the body codes.

MODEL IDENTIFICATION

DESCRIPTION

The computerized engine control system monitors as many as 19 engine/vehicle functions. (Scheme 514) This system controls engine operation and lowers exhaust emissions while maintaining fuel economy and driveability. The Electronic Control Module (ECM) is the "brain" of the CCC system.

The computerized engine control system is primarily an emission control system, designed to maintain a 14.7:1 air/fuel ratio under all operating conditions. When the ideal air/fuel ratio is maintained, the 3-way catalytic converter can control Oxides of Nitrogen (NOx), Hydrocarbon (HC) and Carbon Monoxide (CO) emissions.

ECM Conditions Sensed & Systems Controlled. Scheme 514

OPERATION

The ECM of computerized engine control system is equipped with a self-diagnostic system which detects system failures or abnormalities. As a bulb and system check, "SERVICE ENGINE SOON" light will glow when ignition switch is turned to "ON" position and engine is not running. When engine is started, light should go out. If not, a malfunction has been detected in the computerized engine control system or "SERVICE ENGINE SOON" light circuit is faulty.

When a malfunction occurs, ECM will illuminate the "SERVICE ENGINE SOON" light located on instrument panel. When malfunction is detected and light is turned on, a corresponding trouble code will be stored in ECM memory. 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 the malfunction is repaired. If light comes on and remains on during vehicle operation, cause of malfunction must be determined using diagnostic charts. If a sensor fails, ECM will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is driveable, but loss of good driveability will most likely be encountered.

"Intermittent Failures"

Intermittent failures cause "SERVICE ENGINE SOON" light to flicker or illuminate and go out about 10 seconds after the intermittent fault goes away. The corresponding trouble code, however, will be retained in ECM memory. If related fault does not reoccur within 50 engine restarts, related trouble code will be erased from ECM memory. Intermittent failures may be caused by sensor, connector or wiring related problems. Refer to INTERMITTENT PROBLEMS in the article CEC TESTING W/O CODES (TROUBLE SHOOTING) in the ENGINE PERFORMANCE section.

Note. Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds. Others may require operation for 5 minutes or longer under engine load.

DIAGNOSTIC PROCEDURE

Note. Most computerized 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, ignition high tension wires, fuel supply, electrical connections and vacuum hoses should be checked. Failure to do so may result in lost diagnostic time.

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

1. Make sure that all engine systems not related to the computer system are operating properly. Do not proceed with testing unless all other problems have been repaired.
2. Perform appropriate DIAGNOSTIC CIRCUIT CHECK for that system. If trouble codes were displayed (other than Code 12), decide whether codes are "hard" or "intermittent" trouble codes. "Hard" codes will cause the "SERVICE ENGINE SOON" light to illuminate continuously while engine is running. See «ECM TROUBLE CODE DEFINITIONS»(/oldsmobile/cutlass-ciera/i-1981-1996/remont/testing-diagnostics/#28l-vin-w-pfi-cec-tests-wcodes__ecm-trouble-code-definitions) table in this article.
3. If no trouble codes were displayed, perform FIELD SERVICE MODE CHECK procedures.
4. If no trouble is indicated by the FIELD SERVICE MODE check and/or a driveability problem exists, refer to «DIAGNOSIS & TESTING»(/oldsmobile/cutlass-ciera/i-1981-1996/remont/testing-diagnostics/#28l-vin-w-pfi-cec-tests-wcodes) and/or «SCAN TESTER USAGE»(/oldsmobile/cutlass-ciera/i-1981-1996/remont/testing-diagnostics/#28l-vin-w-pfi-cec-tests-wcodes__scan-tester-usage) in this article.
5. After any repairs are made, clear any trouble codes and perform FIELD SERVICE MODE check again.

Scheme 515

1. Turn ignition on. Do not start engine. "SERVICE ENGINE SOON" light should glow. Locate Assembly Line Data Link (ALDL) connector attached to ECM wiring harness under instrument panel, left or right of steering column. Insert jumper wire across terminal "B", "DIAGNOSTIC TERMINAL" and terminal "A", "GROUND". (Scheme 515) CAUTION: Inserting spade lug (jumper lead) into terminals of ALDL connector grounds "DIAGNOSTIC TERMINAL". Do not ground ALDL connector until after ignition is on (engine not running). (Scheme 515): ALDL Connector Terminal Identification NOTE: In some of the diagnostic and trouble shooting charts the Assembly Line Data Link (ALDL) may also be referred to as the Assembly Line Communication Link (ALCL). These are referring to the same connector. It is also the test point for connection of aftermarket "Scan" testers.
2. "SERVICE ENGINE SOON" light should flash Code "12". Code "12" consists of "FLASH", pause, "FLASH", "FLASH" followed by a longer pause. Trouble Code "12" will be repeated 2 more times. If any other trouble codes are stored in ECM memory, they will be displayed in the same manner.
3. To exit diagnostic mode, turn ignition off and remove jumper wire from ALDL connector.

READING TROUBLE CODES

The ECM stores component failure information for the CCC system under a related trouble code which can be recalled for diagnosis and repair. Trouble codes may be read by counting flashes of the "SERVICE ENGINE SOON" light, or by reading the output of a diagnostic "Scan" tester connected to the ALDL connector. The tester is faster, more accurate, and capable of reading information which otherwise would necessitate testing individual ECM and sensor/solenoid connector terminals with a volt/ohmmeter. Refer to the following

1. «SCAN TESTER - TEST DATA PARAMETERS»(/oldsmobile/cutlass-ciera/i-1981-1996/remont/testing-diagnostics/#28l-vin-w-pfi-cec-tests-wcodes) table.
2. «SCAN TESTER USAGE»(/oldsmobile/cutlass-ciera/i-1981-1996/remont/testing-diagnostics/#28l-vin-w-pfi-cec-tests-wcodes__scan-tester-usage) .

If "Scan" tester is not available, it is possible to read flashes of the dashboard "SERVICE ENGINE SOON" light by grounding the diagnostic terminal of the ALDL with ignition on and engine off. For example, "FLASH", "FLASH", pause, "FLASH", longer pause, identifies "21". The first series of flashes are the first digit of trouble code; second series of flashes are the second digit of trouble code. Trouble codes are displayed starting with the lowest numbered code. Each code is displayed 3 times. Codes will continue to repeat as long as ALDL "DIAGNOSTIC 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 may require operation for 5 minutes or longer at normal operating temperature, road speed and load. Therefore, some codes may not set in a service bay operational mode.

ECM TROUBLE CODE DEFINITIONS

ECM TROUBLE CODE DEFINITIONS

Note. Trouble code charts should only be used 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.

Note. Any time Codes 51, 52, 54 or 55 are displayed with another code, start with "50-series" code first, then proceed to low profile numbered code.

TROUBLE CODE DETERMINATION (HARD OR INTERMITTENT)

During any diagnostic procedure, you must decide between "hard" failure codes and "intermittent" failure codes. Diagnostic charts will not usually help analyze "intermittent" codes. To determine "hard" codes and "intermittent" codes, proceed as follows

1. Manually enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode and clear trouble codes.
2. Apply parking brake and place transmission in Neutral (man. trans.) or "P" (auto. trans.). Block drive wheels. Start engine. "SERVICE ENGINE SOON" light should go out. Run warm engine at specified curb idle for 2 minutes. Note "SERVICE ENGINE SOON" light.
3. If "SERVICE ENGINE SOON" light comes on, enter diagnostic mode. Read and record trouble codes. This will reveal "hard failure" codes. Codes 13, 15, 24, 44, 45 and 55 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". Exceptions are noted under DIAGNOSTIC PROCEDURE.

CLEARING TROUBLE CODES

Turn ignition switch to "ON" position and ground "DIAGNOSTIC TERMINAL" lead at ALDL connector. Turn ignition switch to "OFF" position and remove ECM fuse from fuse block for 10 seconds. Replace fuse. Remove "DIAGNOSTIC TERMINAL" ground lead.

DIAGNOSTIC MATERIALS

Note. The charts described in the following paragraphs are arranged later in this article, by engine size and fuel system type.

Diagnostic Charts

The diagnostic charts are used to find and repair problems which the on-car diagnostics have found. These charts include

1. Charts which test the reliability of the self-diagnostic system.
2. Charts which help fix problems which are "SERVICE ENGINE SOON" light related.
3. Charts which test the computerized fuel control system performance.
4. Charts which help fix a problem when the on-car diagnostics don't work.
5. ENGINE CRANKS BUT WON'T RUN charts. Refer to the appropriate DIAGNOSTIC A-CHARTS in 2.8L VIN [W] PFI "A" CHARTS article.
6. Charts where a stored trouble code leads you to a particular problem. See «ECM TROUBLE CODE DEFINITIONS»(/oldsmobile/cutlass-ciera/i-1981-1996/remont/testing-diagnostics/#28l-vin-w-pfi-cec-tests-wcodes__ecm-trouble-code-definitions) and DIAGNOSTIC AIDS in this section. Charts which are used because the FIELD SERVICE MODE CHECK found a problem.

Note. Although there are many charts connected with computer diagnosis, only 2 charts are needed to prove system is operating properly. Normally, only 3 charts are necessary to find a problem, if one exists.

Diagnostic Aids

Diagnostic aids (located in each "trouble code" chart box for each system) are additional tips used to help diagnose trouble codes when inspected circuit checks out okay. Diagnostic aids may help lead to a definitive solution to that trouble code problem.

Field Service Mode Check (Fuel Injected Models)

On fuel injected models, "SERVICE ENGINE SOON" light will indicate operational mode of engine if ALDL is grounded while engine is running. In closed loop mode, "SERVICE ENGINE SOON" light will flash at a rate of one flash per second. In open loop, light will flash at a rate of 2.5 flashes per second. If light is off all or most of the time, a lean exhaust is indicated. If light is on all or most of the time, a rich exhaust is indicated.

This test confirms proper operation of fuel system and verifies closed loop operation. Clear codes and perform this test after any repair is completed. When performing this check, always engage parking brake and block DRIVE wheels. Parking brake on front-wheel drive models does NOT hold drive wheels.

Note. On some engines, oxygen sensor will cool off after only a short period of time while engine is idling. This will cause engine to go into open loop. To restore closed loop mode, run engine at part throttle several minutes and accelerate from idle to part throttle several times.

SPECIAL DIAGNOSTIC TOOLS

Note. Special "Scan" testers plugged into the ALDL may be used to read trouble codes and check voltages in the system on the serial data line (terminal "E" on EFI and terminal "M" on EFI with P-4 systems). These testers can save a great deal of time. For additional information see SCAN TESTER USAGE and SCAN TESTER - TEST DATA PARAMETERS table in this article.

The computerized engine control system is most easily diagnosed using a "Scan" tester, however, other tools may aid in diagnosing problems if a "Scan" tester is unavailable. These tools are: a tachometer, a dwell meter, test light, ohmmeter, digital voltmeter with 10-megohm impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights (TBI and PFI) and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connector 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.

Note. If engine operation seems to change when dwell meter is connected to Green wire, remove dwell meter and use another type. A few brands are not compatible with computerized engine control system.

When engine is at operating temperature and idling, dwell meter needle should vary between 10-50 degrees. This indicates closed loop operation. Before engine reaches operating temperature, dwell should be fixed between 10-50 degrees, indicating open loop operation. If after reaching normal operating temperature dwell is fixed between 10-50 degrees, less than 10 degrees or more than 50 degrees, refer to appropriate CHART A - DWELL FIXED diagnostic chart for that system in 2.8L VIN [W] PFI "A" CHARTS article.

SCAN TESTER USAGE

Note. Prior to connection of scan tester to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received by scan tester will be accurate. This is done by performing appropriate DIAGNOSTIC CIRCUIT CHECK for that system. If vehicle does not pass diagnostic circuit check, information received by scan tester may be invalid. CCC Scan tester is a specialized tester which, when plugged into ALDL, can be used to diagnose on- board computer control stems by providing instant access to circuit voltage information without need to crawl under dash or hood to back-probe sensors and connectors.

Scan testers cut down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN TESTER - TEST DATA PARAMETERS table. They also furnish information on output device (solenoids and motors) status. Status parameters, however, are only an indication that output signals have been sent to devices by the ECM. It does not indicate if devices have responded properly to that signal. This will need to be verified 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 may not be indicated by all makes of scan tester.

If trouble codes are not present, this is not an indication that there is not a problem. CCC related problems are about 20 percent codes and 80 percent driveability. Sensors that are out of specification WILL NOT set a trouble code but WILL cause driveability problems. Use of a 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 the SCAN TESTER - TEST DATA PARAMETERS table below.

Note. Information obtained by scan tester is only as accurate as the tester itself. If erroneous voltage signals are suspected, it will be necessary to verify tester information using a digital voltmeter and wiring schematic. If non- existent codes are in evidence, turn ignition off, remove tester, turn ignition on and ground ALDL "DIAGNOSTIC TERMINAL". If same codes are not flashed by "SERVICE ENGINE SOON" light that were indicated by scan tester, tester cannot be used on vehicle and information obtained by it will not be guaranteed accurate.

SCAN DATA

Note. Information in the following table is typical 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 virtually instantaneous. Not all devices & systems are used on all models.

SCAN TESTER - TEST DATA PARAMETERS

Note. This ECM voltage chart can be used with a digital voltmeter to help save time in diagnosis. Voltages on the car being tested my vary slightly from these due to battery or alternator charging level.

SYMPTOM FLOW CHARTS ("A" CHARTS)

For "A" Charts see 2.8L VIN [W] PFI "A" CHARTS article.

CHART B1 - RESTRICTED EXHAUST SYSTEM CHECK

Before any components are replaced, exhaust system must be checked for restrictions. Check at AIR pipe or check at O2 sensor procedure may be used to diagnose condition, depending on engine or tool used.

Check At Air Pipe

Remove rubber hose at exhaust manifold AIR pipe check valve and remove check valve. Install fuel pump pressure gauge to hose and nipple via Propane Enrichment Device (J26911) (Scheme 516) Nipple should be inserted into exhaust manifold AIR pipe.

Restricted Exhaust System Check at Air Pipe. Scheme 516

Check At O2 Sensor

Remove O2 sensor. Install back pressure tester in place of O2 sensor as shown in illustration. After test is completed, ensure that O2 sensor threads are coated with anti-seize compound before installation.

Restricted Exhaust System Check at O2 Sensor. Scheme 517

Diagnosis

1. Start engine and bring to operating temperature. Allow engine to idle and observe exhaust system back pressure gauge. Reading should not exceed 1.25 psi (.09 kg/cm 2 ).
2. Increase engine speed to 2000 RPM and note gauge. Reading should not exceed 3 psi (.21 kg/cm 2 ).
3. If during steps 1) or 2), specification is exceeded, exhaust system restriction is indicated.
4. Check complete exhaust system for collapsed pipe, heat distress and possible internal muffler failure.
5. If none of the conditions in step 4) exist, check for restricted catalytic converter. Replace if necessary.

CODE 13 - OPEN OXYGEN SENSOR CIRCUIT

The ECM supplies a voltage of about .45 volt between circuits No. 412 and 413. If measured with a 10-megohm digital voltmeter, this may read as low as .32 volt. The oxygen sensor varies the voltage within a range of about one volt if the exhaust is rich, down to about .10 volt if exhaust is lean. The sensor is like an open circuit and produces no voltage when it is less than 600°F (316°C). An open sensor circuit or cold sensor causes "open loop" operation.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 13 will set when the following conditions occur: Engine at normal operating on temperature. At least 2 minutes elapsed since start-up. Oxygen signal voltage steady between .35 and .55 volt. Throttle angle greater than 5 percent (about .3 volt greater than closed throttle voltage). All conditions must be met for about 60 seconds. If conditions for a Code 13 exist, the system will not go "closed loop".
2. This test will determine if the sensor, wiring or ECM is the cause of Code 13.
3. When conducting this test, use only a high impedance (10-megohm) digital volt/ohmmeter. This test checks the continuity of circuits No. 412 and 413. If circuit No. 413 is open the ECM voltage on circuit No. 412 will be greater than .6 volt.

Normal "Scan" tester voltage varies between 100 and 999 mV while in "closed loop". Code 13 will set in one minute if voltage remains between .35-.55 volt, however, system will go "open loop" in about 15 seconds.

Code 13 Schematic, Oxygen Sensor Circuit. Scheme 518

Code 13, Oxygen Sensor Circuit. Scheme 519

CODE 14 - COOLANT TEMPERATURE SENSOR (CTS) SIGNAL VOLTAGE LOW

The Coolant Temperature Sensor (CTS) uses a thermistor to control the signal voltage to the ECM. The ECM applies and monitors a voltage on circuit No. 410 to the sensor. When the engine is cold, the sensor resistance is high, therefore, the ECM will see high monitored voltage. As the engine warms, the sensor resistance becomes less and the monitored voltage drops. At normal operating temperature, the voltage will measure about 1.5-2.0 volts on circuit No. 410. Coolant temperature is one of the inputs used to control; fuel delivery, spark timing, idle speed, converter clutch, canister purge, air management (man. trans. only), EGR and cooling fan. Code 14 will set if monitored voltage indicates a coolant temperature greater than 275-285°F (134-141°C) for about 3 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 14 will set if signal voltage indicates high coolant temperature for 3 seconds.
2. This test will determine if circuit No. 410 is shorted to ground which will cause the conditions for Code 14.

Check harness routing for a potential short to ground in circuit No. 410. The "Scan" tester displays engine temperature in degrees centigrade. After engine is started, the temperature should rise steadily to about 90°C, then stabilize when thermostat opens.

Code 14 Schematic, Coolant Temperature Sensor Voltage Low. Scheme 520

Code 14, Coolant Temperature Sensor Voltage Low. Scheme 521

CODE 15 - COOLANT TEMPERATURE SENSOR SIGNAL VOLTAGE HIGH

The CTS uses a thermistor to control the signal voltage to the ECM. The ECM applies and monitors voltage on circuit No. 410 to the sensor. When the engine is cold, sensor resistance is high, therefore, the ECM will see a high monitored voltage. As the engine warms, the sensor resistance becomes less and the monitored voltage drops. At normal operating temperature, the voltage will measure about 1.5-2.0 volts on circuit No. 410. Coolant temperature is one of the inputs used to control: fuel delivery, spark timing, idle speed, converter clutch, canister purge, air management (manual transmission), EGR and cooling fan.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 15 will set if signal voltage indicates coolant temperature is less than -47°F (-44°C) for 3 seconds.
2. This test simulates a Code 14. If the ECM recognizes the low signal voltage and the "Scan" tester reads 130°C or more, ECM and wiring are okay.
3. This test will determine if circuit No. 410 is open. There should be 5 volts present at sensor connector if measured with a DVOM.

The "Scan" tester reads engine temperature in degrees centigrade. After engine is started, the temperature should rise steadily to about 90°C, then stabilize when thermostat opens.

A faulty connection, or an open in circuits No. 410 or 452 will result in a Code 15. If Code 22 or 23 is also set, check circuit No. 452 for faulty wiring or connections. Check terminals at sensor for a good contact.

Code 15, Coolant Temperature Sensor Voltage High. Scheme 522

CODE 21 - THROTTLE POSITION SENSOR SIGNAL VOLTAGE HIGH

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to throttle angle. Signal voltage will vary from about .5 volt at idle to about 4.5 volts at wide open throttle. Code 21 will set if the following conditions occur

1. TPS voltage is greater than 2.5 volts for at least 2-5 seconds.
2. Airflow less than 12 gm/sec.
3. Engine speed less than 1200 RPM NOTE: Test numbers refer to test numbers on diagnostic chart.

1. Confirms Code 21 and that fault is present.
2. With TPS sensor disconnected, the TPS voltage should go low if the ECM and wiring are okay.
3. Probing circuit No. 452 with a test light checks the 5-volt return circuit. A faulty 5-volt return will cause a Code 21.

The "Scan" tester reads throttle position in volts. Reading should be less than .54-.56 volt with throttle closed and ignition on or at idle. Voltage should increase at a steady rate as throttle is moved toward WOT. An open in circuit No. 452 will result in a Code 21. Some "Scan" testers measure throttle angle as a percent. A fully closed throttle should read zero percent and a wide open throttle should read 100 percent.

Schematic, TPS Signal Voltage High. Scheme 523

Code 21, TPS Signal Voltage High. Scheme 524

CODE 22 - THROTTLE POSITION SENSOR SIGNAL VOLTAGE LOW

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to throttle angle. Signal voltage will vary from about .5 volt at idle to 4.5 volts at wide open throttle. Code 22 will set if TPS signal voltage is less than about .2 volt for 3 seconds and the engine running.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Confirms Code 22 and that fault is present.
2. Simulates Code 21. If the ECM recognizes the high signal voltage and sets Code 21, the ECM and wiring are okay.
3. With throttle closed, the TPS voltage reading should be at idle specification. See DIAGNOSTIC AIDS below.
4. This simulates a high signal voltage to check for an open in circuit No. 417.

Using a "Scan" tester, reading should be less than .54-.56 volt with throttle closed and ignition on or at idle. Monitored voltage should increase at a steady rate as throttle is moved toward WOT. An open or short to ground in circuits No. 416 or 417 will result in a Code 22. Some "Scan" testers measure throttle angle as a percent. A fully closed throttle should read zero percent and a wide open throttle should read 100 percent.

Code 22, TPS Signal Voltage Low. Scheme 525

CODE 23 - MANIFOLD AIR TEMPERATURE SENSOR SIGNAL VOLTAGE HIGH

The Manifold Air Temperature (MAT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies and monitors voltage on circuit No. 472 to the sensor. When the air is cold, sensor resistance is high and the ECM will see a high monitored voltage. If the air is warm, the sensor resistance is low and ECM will see a low monitored voltage.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 23 will set if signal voltage indicates manifold air temperature is low, time since engine start is more than 4 minutes on and no vehicle speed signal is present (vehicle not moving). Due to the conditions necessary to set a Code 23, the "SERVICE ENGINE SOON" light will only stay on when all 3 conditions are met.
2. A Code 23 will set due to an open sensor, wire or connection. This test will determine if the wiring and ECM are okay. The MAT sensor is difficult to reach on some models so this test can be performed at the MAT sensor harness connector.
3. This will determine if an open is present in the monitored signal circuit No. 472 or the 5-volt return circuit No. 452 ("J" Body), 455 ("A" Body).

The "Scan" tester reads temperature of the air entering the engine (should read close to ambient air temperature when engine is cold) and rises as underhood temperature increases. Carefully check harness and connections for possible open in sensor circuits. Use the TEMPERATURE-TO-RESISTANCE VALUES table to help determine if sensor calibration has shifted.

Code 23 Schematic, MAT Sensor Voltage High ("A" Body). Scheme 526

Code 23, MAT Sensor Voltage High ("A" Body). Scheme 527

Code 23 Schematic, MAT Sensor Voltage High ("J" Body). Scheme 528

CODE 24 - VEHICLE SPEED SENSOR

The ECM applies and monitors 12 volts on circuit No. 437. Circuit No. 437 is connected to the vehicle speed sensor buffer in the instrument cluster. The speed sensor buffer alternately grounds circuit No. 437 when drive wheels are turning. This pulsing action takes place about 2000 times per mile and the ECM will calculate vehicle speed based on the time between pulses. "A" and "J" Bodies use a Hall Effect switch mounted in the speedometer head to signal the VSS buffer.

The "Scan" tester reading should closely match the speedometer reading with drive wheels turning.

Note. Test numbers refer to test numbers on diagnostic chart.

1. To avoid possible damage to CV joints on FWD vehicles, always support control arms whenever drive wheels are turning off of ground. Code 24 will set if vehicle is stopped when the following conditions occur: Reference signal indicates engine speed is between 1400 and 4400 RPM. Throttle angle is less than 2 percent (closed throttle). Low load condition (low airflow or high vacuum). Transmission not in Park or Neutral. All conditions met for 4-5 seconds. These conditions are met during a road load deceleration. Disregard Code 24 that sets when drive wheels are not turning.
2. A voltage of less than one volt at the IP connector indicates that circuit No. 437 is shorted to ground. If after disconnecting circuit No. 437 at the vehicle speed sensor, the voltage reads greater than 10 volts, the vehicle speed sensor is faulty. If voltage remains less than 10 volts, then it is possible that circuit No. 437 wire is grounded. If circuit No. 437 is not grounded, there is a faulty connection at the ECM, or a faulty ECM.

A "Scan" tester should indicate a vehicle speed whenever the drive wheels are turning greater than 3 MPH. A faulty or misadjusted Park/Neutral switch can result in a false Code 24. Use "Scan" tester and check for proper signal while wiggling shifter in Drive.

Code 24 Schematic, Vehicle Speed Sensor ("A" Body). Scheme 529

Code 24 Schematic, Vehicle Speed Sensor ("J" Body). Scheme 530

Code 24, Vehicle Speed Sensor. Scheme 531

CODE 25 - MANIFOLD AIR TEMPERATURE SENSOR SIGNAL VOLTAGE LOW

The Manifold Air Temperature (MAT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies and monitors voltage on circuit No. 472 to the sensor. When manifold air is cold, the sensor resistance is high and the ECM will see a high monitored voltage. As the air warms, the sensor resistance becomes less, and monitored voltage drops. Code 25 will set if monitored voltage indicates manifold air temperature greater than 275°F (134°C) for 3 seconds and time since engine start is 8 minutes or longer. Due to the conditions necessary to set a Code 25, the "SERVICE ENGINE SOON" light will remain on only while the signal is low and vehicle speed is present.

The "Scan" tester reads temperature of the air entering the engine. Parameter should read close to ambient air temperature when engine is cold, and rise as underhood temperature increases). A faulty connection, or an open in the MAT signal or ground circuit will result in a Code 23. Use the TEMPERATURE-TO-RESISTANCE VALUES table and the appropriate Flow Chart/Schematic to help determine if the sensor calibration has shifted.

TEMPERATURE-TO-RESISTANCE VALUES

Code 25 ("A" Body), MAT Sensor Signal Voltage Low. Scheme 532

Code 25, MAT Sensor Signal Voltage Low ("J" Body). Scheme 533

CODE 33 - MASS AIRFLOW (MAF) SIGNAL HIGH ("A" BODY)

The Mass Airflow (MAF) sensor measures the flow of air entering the engine. The sensor produces a frequency output between 32-150 hertz). A large quantity (high frequency) indicates acceleration, and a small quantity (low frequency) indicates deceleration or idle. This information is used by the ECM for fuel control and is converted by "Scan" tester to read airflow in grams per second). A normal reading is about 4-7 grams per second at idle, increasing with RPM. The MAF sensor is powered by the MAF sensor relay (mounted on the left shock tower). MAF sensor should have power supplied to it any time the ignition is on.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 33 will set if the following conditions occur: Ignition on and airflow exceeds 20 grams per second. Engine is running less than 1300 RPM. TPS is 8 percent or less. All the above are met for 2 seconds.

The "Scan" tester cannot be used when diagnosing this code because when Code 33 sets, grams per second will be displaying the default value, however, it may be useful in comparing the signal of a problem vehicle with that of a known good running one.

Code 33, MAF Sensor Signal Voltage High ("A" Body). Scheme 534

CODE 33 - MAP SENSOR SIGNAL HIGH ("J" BODY)

The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The ECM receives this information as a voltage signal which will vary from about 1-1.5 volts at idle (high vacuum/low pressure) to about 4-4.5 volts at wide open throttle (low vacuum/high pressure).

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 33 will set if the following conditions are met: Engine running. Manifold pressure is greater than specified. Throttle angle is less than 2 percent. All conditions have been met for 4-5 seconds. Engine misfire, or a low unstable idle may set a Code 33.
2. With the MAP sensor disconnected, the ECM and "Scan" tester should recognize a low voltage. If low voltage is shown on tester, ECM and harness are not at fault.

An open circuit No. 455 will set a Code 33. Also see CHART C1D - MAP OUTPUT CHECK. If idle is rough or unstable, refer to ROUGH, UNSTABLE, OR INCORRECT IDLE, STALLING in the article CEC TESTING W/O CODES (TROUBLE SHOOTING) in the ENGINE PERFORMANCE section.

Code 33 Schematic, MAP Sensor Voltage High ("J" Body). Scheme 535

Note. If idle is rough, unstable or incorrect, correct before using chart.

Code 33, MAP Sensor Voltage High ("J" Body). Scheme 536

CODE 34 - MASS AIRFLOW SENSOR VOLTAGE LOW ("A" BODY)

The Mass Airflow (MAF) sensor measures the flow of air entering the engine. The sensor produces a frequency output between 32-150 hertz). A large quantity (high frequency) indicates acceleration, and a small quantity (low frequency) indicates deceleration or idle. This information is used by the ECM for fuel control and is converted by "Scan" tester to read airflow in grams per second). A normal reading is about 4-7 grams per second at idle, increasing with RPM. The MAF sensor is powered by the MAF sensor relay (mounted on the left shock tower). MAF sensor should have power supplied to it any time the ignition is on.

Code 34 will set if the engine is running and any of the following conditions occur

1. MAF sensor is disconnected.
2. Relay is faulty.
3. MAF signal circuit is shorted or grounded.
4. Airflow is less than 2 grams per second (low frequency).

A loose or damaged air duct can set Code 34.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks to see if ECM recognizes a problem. A light off at this point indicates an intermittent problem.
2. Checks to see if 5-volt reference signal from ECM is present at MAF sensor harness connector.
3. Checks continuity of electrical circuit at MAF sensor.
4. Checks for open in 12-volt supply.
5. There is a remote possibility that the MAF signal line inside the ECM may be open. Replace the ECM only after all other possibilities have been checked and did not resolve the problem.

The "Scan" tester cannot be used when diagnosing this code because when the code sets, grams per second will be displaying the default value, however, it may be useful in comparing the signal of a problem vehicle with that of a known good running one. Also check for a loose or damaged air duct and foreign material which might have accumulated on sensor.

CODE 34 - MAP SENSOR VOLTAGE LOW ("J" BODY)

The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage which will vary from about 1-1.5 volts at idle (high vacuum/low pressure) to about 4-4.5 volts at wide open throttle (low vacuum/high pressure).

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 34 will set the following conditions are met: Engine speed less than 1200 RPM. Manifold pressure is less than specified. Throttle angle is greater than 20 percent. All conditions have been met for one second.
2. With the MAP sensor jumpered, the ECM and "Scan" tester should recognize a high voltage. If high voltage is shown on tester, ECM and harness are not at fault.
3. Simulates a high signal voltage to check for an open circuit No. 432. If test light is bright during this test, circuit 432 is probably shorted to ground. If "Scan" tester reads greater than 4 volts, circuit No. 474 can be checked by measuring the voltage at terminal "C". Reading should be about 5 volts.

An open circuit No. 432 or 474 will set a Code 34. Also see CHART C1D - MAP OUTPUT CHECK. If idle is rough or unstable, refer to ROUGH, UNSTABLE, OR INCORRECT IDLE, STALLING in the article CEC TESTING W/O CODES (TROUBLE SHOOTING) in the ENGINE PERFORMANCE section.

Code 34, MAP Sensor ("J" Body). Scheme 537

CODE 35 - IDLE SPEED ERROR

Code 35 will set if engine speed is 100 RPM less than or greater than desired (commanded) engine speed for 45 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Continue with test even if engine will not idle. If idle is too low, "Scan" tester will display 80 or more counts, or steps. If idle is high, it will display zero counts. Occasionally an erratic or unstable idle may occur. Engine speed may vary 200 RPM or more up and down. If this occurs, disconnect IAC. If the condition is unchanged, the IAC is not at fault (there is a system problem). Proceed to DIAGNOSTIC AIDS.
2. When the engine was stopped, the IAC valve retracted (more air) to a fixed park position for increased airflow and idle speed during the next engine start. The "Scan" tester will display 80 or more counts.
3. Be sure to disconnect the IAC valve prior to this test. The test light will confirm the ECM signals by a steady or flashing light on all circuits.
4. There is a remote possibility that one of the circuits is shorted to voltage which would have been indicated by a steady light. Disconnect ECM and turn the ignition on, and probe terminals to check for this condition.

A slow unstable idle may be caused by a system problem that cannot be overcome by the IAC. "Scan" tester counts will be greater than 80 counts if idle is too low and zero counts if it's too high.

1. Idle too high Stop engine. Turn ignition on and ground diagnostic terminal. Wait a few seconds for IAC to seat, then disconnect IAC. Start engine. If idle speed is greater than minimum idle specification, locate and correct vacuum leak. If no leak is detected, adjust minimum idle speed.
2. System Too Lean (Air/Fuel Ratio) Idle speed may be too high or low. Engine speed may vary up and down, and disconnecting IAC does not help. This may set Code 44. The "Scan" tester and/or voltmeter will read an oxygen sensor output less than .3 volt. Check for low regulated fuel pressure or water in fuel. A lean exhaust with an oxygen sensor output fixed greater than .8 volt will be a contaminated sensor. This may set Code 45 or 61.
3. System Too Rich (Low Air/Fuel Ratio) Idle speed too low. The "Scan" tester counts usually greater than 80. System is rich and may exhibit Black exhaust smoke. The "Scan" tester and/or voltmeter will read an oxygen sensor signal fixed greater than .8 volt. Check for fuel in pressure regulator hose, high fuel pressure or injector leaking or sticking.
4. MAF Sensor If idle is rough or unstable, disconnect MAF sensor. If idle improves, substitute a known good sensor. MAF sensor may be tested for being out of calibration using MAF Tester (J 36101).
5. Throttle Body Remove IAC and inspect bore for foreign material or evidence of IAC valve dragging the bore.
6. A/C Compressor or Relay Failure If the A/C control relay drive circuit is shorted to ground or if the relay is faulty, an idle problem may exist.

Code 35 Schematic, Idle Speed Error. Scheme 538

Code 35, Idle Speed Error. Scheme 539

CODE 41 - CYLINDER SELECT ERROR

Note. Test numbers refer to test numbers on diagnostic chart.

1. The ECM used for this engine can also be used for other engines. The difference is in the MEM-CAL. If a Code 41 sets, the incorrect MEM-CAL has been installed or MEM-CAL is faulty and must be replaced.

Check MEM-CAL to be sure locking tabs are secure. Also check the pins on both the MEM-CAL and ECM to verify they are making proper contact. Check the MEM-CAL part number for proper application. If the correct MEM-CAL is installed and is defective, it is possible the ECM will also need to be replaced.

Code 41, Cylinder Select Error (Faulty/Incorrect MEM-CAL). Scheme 540

Code 41, Cylinder Select Error (Faulty/Incorrect MEM-CAL). Scheme 541

CODE 42 - EST (WITH DIS)

When the system is running on the ignition module (no voltage on the by-pass line), the ignition module grounds the EST signal. The ECM expects to see no voltage on the EST line during this condition. If it sees voltage, it sets Code 42 and will not go into the EST mode.

When the RPM for EST operation is reached (400 RPM), by-pass voltage is applied. At this time, the EST should no longer be grounded in the ignition module, so the EST voltage should be varying. If the by-pass line is open or grounded, the ignition module will not switch to EST mode, so the EST voltage will be low and Code 42 will be set. If the EST line is grounded, the ignition module will switch to EST, but because the line is grounded, there will be no EST signal and Code 42 will be set.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 42 means the ECM has seen an open or short to ground in the EST or by-pass circuits. This test confirms Code 42 and that the fault causing the code is present.
2. Checks for a normal EST ground path through the ignition module. If EST circuit No. 423 is shorted to ground, it will also read less than 500 ohms. This will be checked later.
3. As the test light voltage touches circuit No. 424, the module should switch, causing the ohmmeter to overrange if the meter is in the 1000-2000 ohms position. Selecting the 10,000-20,000 ohms position will indicate a reading greater than 5000 ohms. The important thing is that the module switched.
4. The module did not switch and this test checks for EST circuit No. 423 for being shorted to ground, by-pass circuit No. 424 open, faulty ignition module connections or module.
5. Confirms that Code 42 is a faulty ECM and not an intermittent in circuits No. 423 or 424.

The "Scan" tester does not have the ability to help diagnose a Code 42 problem. A Mem-Cal not fully seated in the ECM can result in a Code 42.

Code 42 Schematic, EST (With DIS). Scheme 542

Code 42, EST (With DIS). Scheme 543

CODE 43 - ELECTRONIC SPARK CONTROL

The knock sensor is used to detect engine detonation and the ECM will retard the electronic spark timing based on the signal being received. The circuitry within the knock sensor causes the ECM 5-volt reference to be pulled down so that under a no knock condition, circuit No. 496 would measure about 2.5 volts. The knock sensor produces an AC signal. The amplitude and signal frequency is dependent upon the knock level. If circuit No. 496 becomes open or shorted to ground, the voltage will either go to greater than 3.5 volts, or less than 1.5 volts. If either condition occurs, Code 43 will be stored.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Determines if conditions for Code 43 exist (voltage on circuit No. 496 greater than 3.5 volts or less than 1.5 volts). The system is designed to retard spark 6 degrees if either condition exists.
2. The ECM applies and monitors 5 volts on circuit No. 496. This voltage should be present at the knock sensor terminal.
3. Determines if knock sensor resistance is between 330-4500 ohms, sensor is okay.
4. If circuit No. 496 is not open or shorted to ground and the voltage reading is less than 4 volts, the most likely cause is an open circuit inside the ECM. If a replacement ECM did not repair the problem, it is possible a faulty MEM-CAL is drawing the voltage down and should be replaced.

Check for proper installation of MEM-CAL or shorts or opens in circuit No. 496. Also, see INTERMITTENT PROBLEMS in the CEC TESTING W/O CODES (TROUBLE SHOOTING) article in the ENGINE PERFORMANCE section.

Code 43 Schematic, Electronic Spark Control. Scheme 544

Code 43, Electronic Spark Control. Scheme 545

CODE 44 - LEAN EXHAUST INDICATION

The ECM supplies a voltage of about .45 volt between circuits No. 412 and 413. If measured with a 10-megohm digital voltmeter, this may read as low as .32 volt. The oxygen sensor varies the voltage within a range of about one volt if the exhaust is rich, down to about .10 volt if exhaust is lean. The sensor is like an open circuit and produces no voltage when it is less than about 600°F (360°C). An open sensor circuit or cold sensor causes "open loop" operation.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 44 is set when the oxygen sensor signal voltage on circuit No. 412 remains less than .2 volt for at least 60 seconds and the system is operating in "closed loop".

Using the "Scan" tester, observe the block learn values under different RPM and airflow conditions. If the conditions for Code 44 exists, the block learn values will be around 150.

1. Oxygen sensor pigtail may be mispositioned and contacting the exhaust manifold.
2. Check for intermittent ground in wire between connector and sensor.
3. A MAF sensor output that causes the ECM to sense a less than normal airflow will cause the system to go lean. If this occurs, disconnect the MAF sensor. If the lean condition is gone, replace the MAF sensor. MAF Tester (J 36101) may be used to test for an out-of-calibration sensor.
4. Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a false lean exhaust condition and can set a Code 44.
5. System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the vehicle at various speeds. Check fuel volume from pump (one pint in 30 seconds) as well as pressure. Also check rubber fuel lines for internal collapse.
6. If there is an exhaust leak, outside air may be pulled into the exhaust and past the sensor. Vacuum or crankcase leaks can cause A lean condition.
7. If the above tests are okay, replace oxygen sensor.

Code 44, Lean Exhaust Indication. Scheme 546

CODE 45 - RICH EXHAUST INDICATION

The ECM supplies a voltage of about .45 volt between circuits No 412 and 413. The oxygen sensor varies the voltage within a range of about one volt if the exhaust is rich, down to about .10 volt if exhaust is lean. The oxygen sensor is like an open circuit and produces no voltage when it is less than about 600°F (360°C). An open sensor circuit or cold sensor causes "open loop" operation.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 45 is set when the oxygen sensor signal voltage on circuit No. 412 remains greater than .7 volt for 30 seconds, in "closed loop", engine time after start is one minute or more and throttle angle is greater than 2 percent.

Using the "Scan" tester, observe the block learn values at different RPM and airflow conditions. If the conditions for Code 45 exists, the block learn values will be around 115.

1. Fuel system will go rich if pressure is too high. The ECM can compensate for some increase, however, if it gets too high, a Code 45 may be set.
2. Check for fuel contaminated oil.
3. An open ground circuit No. 453 (ignition module ground to ECM) may result in induced electrical "noise". The ECM looks at this "noise" as reference pulses (RPM). The additional pulses result in a higher than actual engine speed signal. The ECM then delivers too much fuel, causing system to go rich. If this problem occurs, "Scan" tester will show a greater than actual engine speed, which can help in diagnosing this problem.
4. Check vapor canister for fuel saturation. If canister is full of fuel, check canister liquid/vapor control and hoses.
5. An output that causes the ECM to sense a higher than normal airflow can cause the system to go rich. Disconnecting the MAF sensor will allow the ECM to set a fixed value for the sensor. Substitute a different MAF sensor, if the rich condition is gone when the sensor is disconnected, or test MAF sensor using MAF Tester (J 36101).
6. Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.
7. An intermittent TPS output will cause the system to go rich due to a false indication of the engine accelerating.

Code 45, Rich Exhaust Indication. Scheme 547

CODE 52 - CALPAK ERROR

Check that all CALPAK/MEM-CAL pins are fully inserted in ECM socket. If okay, replace CALPAK/MEM-CAL. Clear memory and recheck for Code 52. If Code 52 reappears, replace ECM.

CODE 53 - SYSTEM OVERVOLTAGE

This code indicates there is a basic generator problem. Code 53 will set if voltage at the ECM ignition input pin is greater than 17.1 volts for 2 seconds. Check and repair charging system.

CODE 54 - FUEL PUMP VOLTAGE LOW ("A" BODY)

Fuel pump circuit No. 120 is monitored by the ECM and is used to compensate fuel delivery based on system voltage. This signal is also used to store a trouble code if the fuel pump relay is defective or if fuel pump voltage is lost while the engine is running. There should be about 12 volts on circuit No. 120 for 2 seconds after the ignition is turned on, or any time references pulses are being received by the ECM.

Code 54 will set if the voltage on circuit No. 120 is less than 2 volts for 1.5 seconds since the last reference pulse is cycled off, however, if the voltage is detected less than 2 volts with the engine running, the light will only remain on while the condition exists.

Code 54 Schematic, Fuel Pump Voltage Low ("A" Body). Scheme 548

Code 54, Fuel Pump Voltage Low ("A" Body) (1 Of 2). Scheme 549

Code 54, Fuel Pump Voltage Low ("A" Body) (2 Of 2). Scheme 550

CODE 54 - FUEL PUMP VOLTAGE LOW ("J" BODY)

Fuel pump circuit No. 120 is monitored by the ECM and is used to compensate fuel delivery based on system voltage. This signal is also used to store a trouble code if the fuel pump relay is defective or if fuel pump voltage is lost while the engine is running. There should be about 12 volts on circuit No. 120 for 2 seconds after the ignition is turned on, or any time reference pulses are being received by the ECM.

Code 54 will set if the voltage on circuit No. 120 is less than 2 volts for 1.5 seconds since the last reference pulse is cycled off, however, if the voltage is detected less than 2 volts with the engine running, the light will only remain on while the condition exists.

Code 54 Schematic, Fuel Pump Voltage Low ("J" Body). Scheme 551

Code 54, Fuel Pump Voltage Low ("J" Body). Scheme 552

CODE 61 - DEGRADED O2 SENSOR

If a Code 61 is stored in memory, the ECM has determined the Oxygen (O2) sensor is contaminated or degraded because the voltage change time (cross counts) is slow or sluggish.

The ECM performs the O2 sensor response time test when the coolant temperature is more then 185°F (85°C), MAT temperature is greater than 50°F (10°C), system is in "closed-loop" or in a "decel" fuel cut-off mode. If Code 61 is stored, replace the O2 sensor.

CODE 63 - MAP SENSOR VOLTAGE HIGH ("A" BODY)

The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage that varies from about 1-1.5 volts at idle (high vacuum) to 4-4.5 volts at wide open throttle (low vacuum).

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 63 will set when the following conditions occurs: Engine is running. Manifold pressure greater than 22 in. Hg vacuum with A/C off and 24 in. Hg vacuum with A/C on. Throttle angle less than 2 percent. Conditions met for 2 seconds. Engine misfire or a low unstable idle may set Code 63.
2. With the MAP sensor disconnected, the ECM should see a low voltage if the ECM and wiring is okay.
3. See HOW TO USE THIS TROUBLE SHOOTING ARTICLE in the article CEC TESTING W/O CODES (TROUBLE SHOOTING) in the ENGINE PERFORMANCE section.

An open in circuit No. 455 or the connection, will result in a Code 63. With ignition on and engine off, voltage should be within the values shown in the IGNITION ON ENGINE STOPPED VOLTAGES table. Also see CHART C1D - MAP OUTPUT CHECK in 2.8L VIN [W] PFI "C" CHARTS.

Code 63, MAP Voltage High ("A" Body). Scheme 553

CODE 64, MAP SENSOR VOLTAGE LOW ("A" BODY)

The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage that varies from about 1-1.5 volts at idle (high vacuum) to 4-4.5 volts at wide open throttle (low vacuum).

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 64 will set if the following conditions occur: Engine speed less than 600 RPM. Manifold pressure reading less than 4 in. Hg vacuum. Conditions met for one second or engine speed more than 600 RPM. Throttle angle more than 20 percent.
2. This tests to see if sensor is at fault for the low voltage, of if there is an ECM or wiring problem.
3. This test simulates a high signal voltage to check for an open in circuit No. 432. If the test light is bright during this test, circuit 432 is probably shorted to ground. If "Scan" tester reads greater than 4 volts at this test, circuit No. 474 can be checked by measuring the voltage at terminal "C" (should be about 5 volts).

An intermittent open in circuits No. 432 or 474 will set Code 64. With ignition on and engine off, voltage should be within the values shown in the IGNITION ON, ENGINE STOPPED VOLTAGES table. Also see CHART C1D - MAP OUTPUT CHECK in 2.8L VIN [W] PFI "C" CHARTS.

Code 64, MAP Voltage Low ("A" Body). Scheme 554

COMPONENT CHECK FLOW CHARTS (C CHARTS)

For "C" Charts see 2.8L VIN [W] PFI "C" CHARTS article.

Component Locations ("A" Body). Scheme 555

Component Locations ("J" Body). Scheme 556

ECM Terminal Identification ("A" Body). Scheme 557

ECM Terminal Identification ("J" Body). Scheme 558

Wiring Diagram, ("A" Body). Scheme 559

Wiring Diagram, ("J" Body - Cavalier). Scheme 560

Wiring Diagram, ("J" Body - Cimarron). Scheme 561

See also:
• ECM TROUBLE CODE DEFINITIONS
• DIAGNOSIS & TESTING
• SCAN TESTER USAGE