5.0l VIN [e] Tbi Tests W/codes Chevrolet Camaro III рестайлинг

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 64) 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 64

DIAGNOSTIC SYSTEM OPERATION

Note. On EFI models, the "SERVICE ENGINE SOON" lamp driver is built into the ECM. This driver turns on light when ignition is turned on. When vehicle starts, ECM turns light off. If ECM malfunctions or senses malfunction, light will turn back on.

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 TESTS W/O CODES 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.

BASIC 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 table in this article.
3. If no trouble codes were displayed, proceed to appropriate FIELD SERVICE MODE CHECK.
4. If no trouble is indicated by the FIELD SERVICE MODE CHECK procedures and/or a driveability problem exists, refer to TROUBLE SHOOTING in the CEC TESTS W/O CODES article in the ENGINE PERFORMANCE section and/or SCAN TESTER USAGE in this article. Comments there will send you to the proper component charts or tell you the most likely system/component to check.
5. After any repairs are made, clear any trouble codes and perform the FIELD SERVICE MODE check again.

Scheme 65

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 (under cigar lighter plate in center console on Fiero). Insert jumper wire across terminal "B", "DIAGNOSTIC TERMINAL" and terminal "A", "GROUND". (Scheme 65) 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 65): 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. See SCAN TESTER - TEST DATA PARAMETERS table and SCAN TESTER USAGE in this article.

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 DEFINITION

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 BASIC 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 TROUBLE SHOOTING in the CEC TESTS W/O CODES article in the ENGINE PERFORMANCE section.
6. Charts where a stored trouble code leads you to a particular problem. See ECM TROUBLE CODE DEFINITION and DIAGNOSTIC AIDS in this article. 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") These testers can save a great deal of time. For additional information see SCAN TESTER USAGE and SCAN TESTER - TEST DATA PARAMETERS tables 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, 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.

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 in this article. 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 SCAN TESTER - TEST DATA PARAMETERS table in this article.

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 TESTER - TEST DATA PARAMETERS

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.

THROTTLE BODY INJECTION

"NON-SCAN" DIAGNOSTIC CIRCUIT CHECK

The diagnostic circuit check is an organized approach for identifying a problem caused by the fuel injection system. Driver complaints fall into 3 categories: steady "SERVICE ENGINE SOON" light, driveability problems, and "engine cranks, but will not run". Understanding chart and using it correctly will reduce diagnostic time and prevent unnecessary replacement of parts.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. A steady "SERVICE ENGINE SOON" light with ignition on and engine not running confirms battery and ignition voltage to Electronic Control Module (ECM).
2. Ground diagnostic test terminal by connecting a jumper wire between terminals "A" and "B" in assembly line communication link (ALCL) connector, located below instrument panel. The ECM will cause "SERVICE ENGINE SOON" light to flash Code 12, indicating that ECM diagnostics are working. Code 12 will flash 3 times, followed by other trouble codes stored in memory. Each additional code will flash 3 times, starting with lowest code, and then start over again with Code 12. If there are no other codes, Code 12 will flash until diagnostic test terminal jumper is disconnected or engine is started.
3. Record all stored codes, except Code 12. If the problem is "engine cranks but will not run", proceed to CHART A3.
4. If no additional codes were recorded, see TROUBLE SHOOTING procedures in CEC TESTS W/O CODES article in this section for driveability symptoms and recommended service procedures. With engine running and diagnostic terminal grounded, the ECM will respond to the oxygen sensor signal and use the "SERVICE ENGINE SOON" light to display the following information: Closed loop confirms that oxygen sensor signal is being used by the ECM to control fuel delivery and that system is working properly. Signal voltage will vary from below .35 to above .55 volts. Open loop indicates that oxygen sensor signal is not useable to ECM. Signal voltage will be constant and between 35 and .55 volts. System will flash "open loop" for 30 seconds to 2 minutes after engine starts or until sensor reaches normal operating temperature. If system fails to go into closed loop, see Code 13 test. "SERVICE ENGINE SOON" light off indicates that exhaust is lean. Oxygen sensor will be less than .35 volts and steady. See Code 44 test procedures. "SERVICE ENGINE SOON" light on steady indicates that exhaust is rich. Oxygen sensor signal will be above .55 volts and steady. See Code 45 test procedures.
5. Road test of the system in the field service mode should be done only at steady road speeds. The following conditions may be observed and should be considered normal: light on too long under acceleration, light off too long under deceleration or light on too long with idle below 1200 RPM.
6. To clear codes, turn ignition off and disconnect battery pigtail for 10 seconds

"Non-Scan" Diagnostic Circuit Check. Scheme 66

"SCAN" DATA DIAGNOSTIC CIRCUIT CHECK

The Diagnostic Circuit Check is an organized approach to identifying a problem created by an Electronic Engine Control System (EECS) malfunction. It must be the starting point for driveability complaint diagnosis, because it directs the service technician to the next logical step in diagnosing the complaint.

The "SCAN DATA" chart may be used for comparison, after completing the diagnostic circuit check and finding the on-board diagnostics functioning properly and no trouble codes displayed. The typical values are an average of display values recorded from normally operating vehicles and are intended to represent what a normally functioning system would typically display.

Note. A "SCAN" tester that displays faulty data should not be used, and the problem should be reported to the manufacturer. The use of a faulty "SCAN" tester can result in misdiagnosis and unnecessary parts replacement.

Only the parameters listed are used in this article for diagnosis. If a "SCAN" tester reads other parameters, the values are not recommended by General Motors for use in diagnosis.

"Scan" Data Diagnostic Circuit Check. Scheme 67

CHART A1 - NO "SERVICE ENGINE SOON" LIGHT

There should always be a steady "SERVICE ENGINE SOON" light, when the ignition is on and engine stopped. Battery voltage is supplied directly to the light. The electronic control module (ECM) will control the light and turn it on by providing a ground path through circuit No. 419 to the ECM.

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

1. Battery voltage at circuit No. 340 is protected by a 20-amp in-line fuse. If this fuse was blown, refer to wiring schematic for Code 54 test procedures.
2. Using a test light connected to 12 volts, probe each of the system ground circuits to be sure a good ground is present. See ECM terminal end view in this article.

ENGINE RUNS OKAY, CHECK THE FOLLOWING

1. Faulty light bulb.
2. Circuit No. 419.
3. Gauge fuse blown. This will result in no oil, or alternator lights, seat belt reminder etc.

CRANKS, BUT WILL NOT RUN, CHECK THE FOLLOWING

1. Continuous battery drain-fuse or fusible link open.
2. ECM ignition fuse open.
3. Battery circuit No. 340-to-ECM open.
4. Ignition circuit No. 439 to ECM open.
5. Poor connection to ECM.

Chart A1 Schematic, No "Service Engine Soon" Light. Scheme 68

Flow Chart A1, No "Service Engine Soon" Light. Scheme 69

Flow Chart A1, No "Service Engine Soon" Light. Scheme 70

WON'T FLASH CODE 12 "SERVICE ENGINE SOON" ("SES") LIGHT ON STEADY

There should always be a steady "SERVICE ENGINE SOON" light, when ignition is on and engine stopped. Battery voltage is supplied directly to the light bulb. The ECM will turn the light on by grounding circuit No. 419 at the ECM. With the diagnostic terminal grounded, the light should flash a Code 12, followed by any trouble Code stored. A steady light could be a short to ground in light control circuit No. 419, or an open in diagnostic circuit No. 451.

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

1. If there is problem with the ECM that causes a "SCAN" tester not read "Serial Data", then the ECM should not flash a Code 12. If Code 12 does flash, be sure that the "SCAN" tester is working properly on another vehicle. If the "SCAN" tester is functioning properly and circuit No. 461 is okay, the Mem-Cal or ECM may be at fault for the NO ALDL.
2. If the light goes off when the ECM connector is disconnected, then circuit No. 419 is not shorted to ground.
3. This test checks for an open diagnostic circuit No. 451.
4. At this point, the "SERVICE ENGINE SOON" light wiring is okay. The problem is a faulty ECM or PROM. If code 12 does not flash, the ECM should be replaced using the original PROM. Replace the PROM only after trying an ECM, as a defective PROM is an unlikely cause of the problem.

Flow Chart A2, Won't Flash Code 12, "SES" Light On Steady. Scheme 71

Flow Chart A2, Won't Flash Code 12, "SES" Light On Steady. Scheme 72

CHART A3 (1 OF 2) - ENGINE CRANKS BUT WON'T RUN

Note. Before performing this test, check battery condition (12 volts), engine cranking speed, and for adequate fuel in tank.

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

1. A "SERVICE ENGINE SOON" light on is a basic test to determine if there is a 12-volt supply to the ECM. No ALDL may be due to an ECM problem and CHART A2 will diagnose the ECM. If TPS is over 2.5 volts, the engine may be into the clear flood mode which will cause starting problems. The engine will not start without reference pulses and therefore, the "SCAN" tester should read RPM (reference) during cranking.
2. No spark may be caused by one of several components related to the ignition system. CHART C-4 will address all problems related to the causes of a no spark condition.
3. Fuel spray from the injectors indicates that fuel is available. However, the engine could be severely flooded due to too much fuel.
4. While cranking engine, there should be no fuel spray with injector disconnected. Replace an injector if it sprays fuel or drips like a leaking water faucet.
5. The fuel pressure will drop after the fuel pump stops running due to a controlled bleed in the fuel system. Use of the fuel pressure gauge will determine if fuel system pressure is enough for engine to start and run.
6. No fuel spray from injector indicates a faulty fuel system or no ECM control of injector.
7. This test will determine if the ignition module is not generating the reference pulse, of if the wiring or ECM are at fault. Using a test light connected to 12-volts, touch circuit No. 430, a reference pulse should be generated. If injector test light blinks, the ECM and wiring are okay.

Water or foreign material can cause a no start during freezing weather. An EGR sticking open can cause a low air/fuel ratio during cranking. Low fuel pressure can result in a very lean/air fuel ratio. A grounded circuit No. 423 (EST) may cause a no start or a start then stall condition.

Chart A3 Schematic, Cranks But Won't Run ("B" & "G" Bodies). Scheme 73

Chart A3 Schematic, Cranks But Won't Run ("F" Body). Scheme 74

Flow Chart A3, Engine Cranks But Won't Run (1 Of 2). Scheme 75

Flow Chart A3, Engine Cranks But Won't Run (1 Of 2). Scheme 76

CHART A3 (2 OF 2) - ENGINE CRANKS BUT WON'T RUN

This test assumes that battery condition and engine cranking speed are okay, and there is adequate fuel in the tank.

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

1. No fuel spray from one injector indicates a faulty fuel injector or no ECM control of injector. If the test light blinks while cranking, then ECM control should be considered okay. Be sure test light makes good contact between connector terminals during test. The light may be a little dim when its blinking. This is due to current draw of the test light. How bright the blinks is not important.
2. Circuits No. 481 and 482 supply ignition voltage to the injectors. Probe each connector terminal with test light to ground. There should be a light on at one terminal. If the test light confirms ignition voltage at the connector, the ECM injector control circuits No. 467 and 468 may be open. Reconnect the injector and using a test light connected to ground, check at the applicable ECM connector terminal "D14" or "D16". A light at this point indicates that the injector drive circuit is okay. If an ECM repeat failure has occurred, the injector is shorted. Replace the injector and ECM.

Flow Chart A3, Engine Cranks But Won't Run (2 Of 2). Scheme 77

Flow Chart A3, Engine Cranks But Won't Run (2 Of 2). Scheme 78

CHART A7 (1 OF 2) - FUEL SYSTEM DIAGNOSIS

When the ignition switch is on, the ECM will turn on the in-tank fuel pump. It will remain on as long as the engine is cranking or running and the ECM is receiving ignition reference pulses.

If there are no reference pulses, the ECM will shut off the fuel pump within 2 seconds after the key is turned on. The pump will deliver fuel to the TBI unit, where the system pressure is controlled to 9-13 psi (6.2-9.0 kg/cm 2 ). Excess fuel is then returned to the fuel tank. The fuel pump test terminal is located in the left side of the engine compartment. When the engine is stopped, the pump can be turned on by applying battery voltage to the test terminal.

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

1. Fuel pressure should be noted while fuel pump is running. Fuel pressure will drop immediately after fuel pump stops running due to a controlled bleed in the fuel system.

Improper fuel system pressure can result in of the following problems

CRANKS, BUT WON'T RUN.

1. Code 44.
2. Code 45.

CUTS OUT, MAY FEEL LIKE AN IGNITION PROBLEM.

1. Poor fuel economy, loss of power.
2. Hesitation.

Chart A7 - Electrical Schematic, Fuel System Diagnosis. Scheme 79

Chart A7 - Fuel System Schematic. Scheme 80

Flow Chart A7 (1 Of 2), Fuel System Diagnosis. Scheme 81

CHART A7 (2 OF 2) - FUEL SYSTEM DIAGNOSIS

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

1. Has regulated fuel pressure, but pressure is less than 9 psi (.6 kg/cm 2 ). Check the following when this condition occurs: Amount of fuel to injectors is okay, but pressure is too low. Fuel system will be running lean and may set Code 44. Also exhibits hard starting cold and poor overall performance. Has restricted fuel flow causing pressure drop. Normally, a vehicle with a fuel pressure of less than 9 psi (6.2 kg/cm 2 ) at idle will not be driveable. However, if the pressure drop occurs only while driving, the engine will normally surge, then stop, as pressure begins to drop rapidly.
2. Restricting the fuel return line allows the fuel pump to develop its maximum pressure (dead head pressure). When battery voltage is applied to the fuel pump test terminal, pressure should be 13-18 psi (90-124 kg/cm 2 ).
3. This test determines if the high fuel pressure is due to a restricted fuel return line or throttle body pressure regulator malfunction.

Flow Chart A7 (2 Of 2) Fuel System Diagnosis. Scheme 82

CODE 13 - OPEN OXYGEN (O2) SENSOR CIRCUIT

The ECM supplies voltage of about .45 volt between terminals D7 and D6. If measured with a 10-megohms digital voltmeter, this may read as low as .32 volts. The oxygen sensor varies the voltage within a range of about one volt (rich exhaust) to .1 volt (lean exhaust). The oxygen sensor is like an open circuit and produces no voltage when it is below about 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 if the following conditions occur: Engine at normal operating temperature. At least 2 minutes engine running time after start. Oxygen signal voltage steady between .35 and .55 volts. RPM above 1600. Throttle position sensor signal above 5% (about .3 volts above closed throttle). All conditions must be met for about 60 seconds. If the conditions for a Code 13 exists, the system will not go into "closed loop".
2. This will determine if the sensor is at fault, wiring or ECM is the cause of the Code 13.
3. In doing this test, use only a high impedance 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 over .6-volts.

Normal "SCAN" tester voltage varies between .1-1.0-volts, but the system will go "open loop" in about 15 seconds.

Code 13 Schematic: Open Oxygen (O2) Sensor Circuit. Scheme 83

Flow Chart, Code 13: Open Oxygen (O2) Sensor Circuit. Scheme 84

Flow Chart, Code 13: Open Oxygen (O2) Sensor Circuit. Scheme 85

CODE 14 - COOLANT SENSOR (TEMPERATURE TOO HIGH)

The coolant temperature sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies voltage on circuit No. 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore the ECM will see high signal voltage.

As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature the voltage will measure about 1.5-2.0 volts.

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

Note. The "SCAN" tester displays engine temperature in degrees centigrade.

1. Code 14 will set if, signal voltage indicates a coolant temperature above 275°F (135°C) for 2 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. After engine is started, the temperature should rise steadily to about 90°C, then stabilize when thermostat opens.

Code 14 Schematic: Coolant Sensor Circuit. Scheme 86

Flow Chart, Code 14: Coolant Sensor (Temperature Too High). Scheme 87

Flow Chart, Code 14: Coolant Sensor (Temperature Too High). Scheme 88

CODE 15 - COOLANT SENSOR (TEMPERATURE TOO LOW)

The coolant temperature sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on circuit No. 410 to the sensor. When engine is cold the sensor (thermistor) resistance is high, therefore the ECM will see high signal voltage.

As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature the voltage will measure about 1.5-2.0 volts at the ECM.

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

Note. The "SCAN" tester displays engine temperature in degrees centigrade.

1. Code 15 will set if the following conditions occur: Engine running longer than 30 seconds. Coolant temperature less than -22°F (-30°C), for 3 seconds.
2. This test simulates a Code 14. If the ECM recognizes the low signal voltage, (high temperature) and the "SCAN" tester reads above 130°C, the 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 as measured with a digital volt/ohmmeter.

A "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.

If Code 21 is also set, check circuit No. 452 for faulty wiring or connections. Check terminals at sensor for good contact.

Flow Chart, Code 15: Coolant Sensor (Temperature Too Low). Scheme 89

Flow Chart, Code 15: Coolant Sensor (Temperature Too Low). Scheme 90

CODE 21 - TPS SIGNAL VOLTAGE HIGH

The throttle position sensor (TPS) provides a voltage signal that changes the relative signal voltage to the throttle valve. Signal voltage will vary from less than 1.25 volts at idle to 4.5 volts at wide open throttle. Code 21 will set if: TPS voltage is greater than 2.5 volts for 5 seconds, engine speed is less than 1200 RPM or if MAP is less than 9 psi (no load condition).

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

1. Code 21 will set if: TPS signal voltage is greater than 2.5 volts. All conditions are met for 8 seconds. MAP is less than 10 psi (5.2 kg/cm 2 ).
2. With the TPS sensor disconnected, the TPS voltage should drop if the ECM and wiring are okay.
3. Using a test light, probe circuit No. 452. This checks the 5-volt return circuit. If there's a faulty 5-volt return, a Code 21 will be set.

The "SCAN" tester reads throttle position in volts. Reading should be less than 1.25 volts 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.

Code 21 Schematic: TPS Signal Voltage High. Scheme 91

Flow Chart, Code 21: TPS Signal Voltage High. Scheme 92

Flow Chart, Code 21: TPS Signal Voltage High. Scheme 93

CODE 22 - TPS SIGNAL VOLTAGE LOW

The throttle position sensor (TPS) provides a voltage signal that changes relative to throttle valve position. Signal voltage will vary from less than 1.25 volts at idle to 4.5 volts at wide open throttle. Code 22 will set if engine is running, TPS voltage is less than .2 volts for 5 seconds and engine speed is less than 1200 RPM. Possible causes of Code 22 are a faulty TPS, wiring, terminals or ECM.

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

1. Code 22 will set if the following conditions occur: Engine is running. TPS signal voltage is less than about .2 volts for 2 seconds.
2. This step simulates Code 21. If the ECM recognizes the high signal voltage, the ECM wiring is okay.
3. This simulates a high signal voltage to check for an open in circuit No. 417. The "SCAN" tester will not read up to 12 volts, but the ECM will recognize voltage at circuit No. 417.
4. There should be 5 volts at terminal "C" if measured with a digital volt/ohmmeter (DVOM) when ignition is on.

A "SCAN" tester reads throttle position in volts. Reading should be less than 1.25 volts with throttle closed and ignition on or at idle. 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. If Code 22 is also set, check circuit No. 416 carefully for open or short to ground.

Flow Chart, Code 22: TPS Signal Voltage Low. Scheme 94

Flow Chart, Code 22: TPS Signal Voltage Low. Scheme 95

CODE 23 - MAT SENSOR TEMPERATURE LOW

The MAT sensor uses a thermistor to control the signal voltage to the ECM. The ECM supplies and monitors a voltage signal (4-6 volts) to the sensor through circuit No. 472. When temperatures are low, sensor resistance is high and the ECM will see a high voltage signal. As temperatures increase, sensor resistance decreases and the voltage sensed by the ECM drops.

Code 23 will set if the engine has been running for more than 2 minutes and the signal voltage indicates a MAT temperature of less than 292°F (-34°C). A Code 23 will also result if circuits No. 472 or 469 become open.

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

1. Checks to see if Code 23 is the result of a hard failure or an intermittent condition.
2. Simulates conditions for a Code 25. If the "Scan" tester displays a high temperature, the ECM and wiring are not at fault.
3. Checks for continuity of circuits No. 472 and 469. If circuit No. 469 is open there may also be a Code 33 stored.

If the engine is allowed to cool overnight, the coolant and MAT sensors, when measured with a "Scan" tester, should read close to each other. When Code 15 is set, the ECM will turn on the cooling fan.

Code 23 Schematic: MAT Sensor Temp Low. Scheme 96

Flow Chart, Code 23: MAT Sensor Temp Low. Scheme 97

Flow Chart, Code 23: MAT Sensor Temp Low. Scheme 98

CODE 24 - VEHICLE SPEED SENSOR ("B" & "G" BODIES)

The ECM applies and monitors 12 volts on circuit No. 437. Circuit No. 437 connects to the vehicle speed sensor which alternately grounds circuit No. 437 when vehicle is in motion. This pulsing action takes place about 2000 times per mile and the ECM will calculate vehicle speed based on the time between "pulses".

With vehicle in motion, the "SCAN" tester reading should closely match with speedometer reading. Disregard a Code 24 set when vehicle is not in motion.

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

1. Code 24 will set if vehicle speed equals zero mph when the following conditions occur: Engine speed is between 1200-4400 RPM. TPS is less than 2% (closed throttle). Low load condition (high vacuum). Less than 8 psi (2.5 kg/cm 2 ). All conditions met for 5 seconds. If these conditions are met during a road load deceleration, disregard Code 24 that sets when vehicle is not in motion.
2. When there is 8-12 volts at the IP connector, this indicates circuit No. 437 is open between IP connector and the VSS, or there is a faulty vehicle speed sensor. 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 above 10 volts, the vehicle speed sensor is faulty. If voltage remains less than 8 volts, then circuit No. 437 is grounded. If circuit No. 437 is not grounded, there is a faulty connection at the ECM, or a faulty ECM unit.

A "SCAN" tester should indicate a vehicle speed whenever the vehicle is not in motion. A faulty or misadjusted Park/Neutral switch can result in a false Code 24. Use "SCAN" tester and check for proper signal while in drive.

Code 24 Schematic: Vehicle Speed Sensor ("B" & "G" Bodies). Scheme 99

Flow Chart, Code 24: Vehicle Speed Sensor ("B" & "G" Bodies). Scheme 100

Flow Chart, Code 24: Vehicle Speed Sensor ("B" & "G" Bodies). Scheme 101

CODE 24 - VEHICLE SPEED SENSOR ("F" BODY)

The ECM applies and monitors 12 volts on circuit No. 437. Circuit No. 437 connects to the vehicle speed sensor which alternately grounds circuit No. 437 when vehicle is in motion. This pulsing action takes place about 2000 times per mile and the ECM will calculate vehicle speed based on the time between "pulses".

With vehicle in motion, the "SCAN" tester reading should closely match with speedometer reading. Disregard a Code 24 set when vehicle is not in motion.

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

1. Code 24 will set if vehicle speed equals zero mph when the following conditions occur: Engine speed is between 1200-4400 RPM. TPS is less than 2% (closed throttle). Low load condition (high vacuum). Less than 8 psi (2.5 kg/cm 2 ). All conditions met for 5 seconds. If these conditions are met during a road load deceleration, disregard Code 24 that sets when vehicle is not in motion.
2. When there is 8-12 volts at the IP connector, this indicates circuit No. 437 is open between IP connector and the VSS, or there is a faulty vehicle speed sensor. 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 above 10 volts, the vehicle speed sensor is faulty. If voltage remains less than 8 volts, then circuit No. 437 is grounded. If circuit No. 437 is not grounded, there is a faulty connection at the ECM, or a faulty ECM unit.

A "SCAN" tester should indicate a vehicle speed whenever the vehicle is not in motion. A faulty or misadjusted Park/Neutral switch can result in a false Code 24. Use "SCAN" tester and check for proper signal while in drive.

Code 24 Schematic: Vehicle Speed Sensor ("F" Body). Scheme 102

Flow Chart, Code 24: Vehicle Speed Sensor ("F" Body). Scheme 103

Flow Chart, Code 24: Vehicle Speed Sensor ("F" Body). Scheme 104

CODE 25 - MAT SENSOR TEMPERATURE HIGH

The MAT sensor uses a thermistor to control the voltage signal to the ECM. The ECM applies and monitors a voltage signal (4-6 volts) to circuit No. 472. When manifold air is cold, the sensor resistance is high and the ECM will see a high signal voltage. As air warms, resistance decreases and voltage sensed by the ECM drops. Sensor resistance can be measured at ECM terminals "B5" and "W14".

Code 25 will set if a MAT temperature greater than 275°F (135°C) is sensed for more than 2 seconds. A Code 25 will also result if circuit No. 472 is shorted to ground.

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

1. This test checks to determine if the code is a hard failure or an intermittent condition.

If the engine is allowed to cool overnight, the coolant and MAT sensors, when measured with a "Scan" tester, should read close to each other.

Flow Chart, Code 25: MAT Sensor Temperature Too High. Scheme 105

Flow Chart, Code 25: MAT Sensor Temperature Too High. Scheme 106

CODE 32 - EGR SYSTEM FAILURE (1987 MODELS)

The ECM operates a solenoid to control the EGR valve. This solenoid is normally closed. By providing a ground path, the ECM energizes the solenoid which then allows vacuum to pass to the EGR valve.

The ECM monitors EGR effectiveness by de-energizing the EGR control solenoid, thereby shutting off vacuum to the EGR valve diaphragm. With EGR valve closed, manifold vacuum will be greater than it was during normal EGR operation and this change will be relayed to ECM by the MAP sensor. If the change is not within the calibrated window, Code 32 will be set if the following conditions occurs

1. Vehicle speed is above 50 mph.
2. Engine vacuum is between 8-13 in. Hg.
3. No change in throttle position while test is being run.

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

1. Checks for solenoid stuck open.
2. Checks for solenoid always being energized.
3. Grounding test terminal should energize solenoid and vacuum should drop.
4. Negative backpressure valve should hold vacuum with engine off.
5. When engine is started, exhaust backpressure should cause vacuum to bleed off and valve to fully close.

Vacuum lines should be thoroughly checked for internal restrictions. The ECM uses the MAP sensor for checking EGR operation.

Code 32 Schematic: EGR System Failure (1987, All Models). Scheme 107

Flow Chart, Code 32: EGR System Failure (1987, All Models). Scheme 108

Flow Chart, Code 32: EGR System Failure (1987, All Models). Scheme 109

CODE 32 - EGR SYSTEM FAILURE (1988 MODELS)

The ECM operates a solenoid to control the EGR valve. This solenoid is normally closed. By providing a ground path, ECM energizes solenoid, allowing vacuum to pass to the EGR valve. The ECM monitors EGR effectiveness by occasionally de-energizing the EGR control solenoid, shutting off vacuum to the EGR valve diaphragm. With EGR valve closed, manifold vacuum will be greater than it was during normal EGR operation. This change will be relayed to ECM by the MAP sensor. Code 32 will be set if the change is not within the calibrated window and vehicle speed is greater than 50 MPH, engine vacuum is between 8-13 in. Hg and no change in throttle position occurs while test is being run.

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

1. Checks for solenoid stuck open.
2. Checks for solenoid always energized.
3. Grounding ALDL "test" terminal should energize solenoid and vacuum should drop.
4. Negative backpressure valve should hold vacuum with engine off.
5. When engine is started, exhaust backpressure should cause vacuum to bleed off and valve to fully close.

Engine has a manifold vacuum source which should supply at least 7 in. Hg vacuum at idle. Vacuum lines should be checked for internal restrictions. The ECM uses the MAP sensor signal for checking EGR operation. Also see CHART C1D - MAP OUTPUT CHECK.

Flow Chart, Code 32: EGR System Failure (1988, All Models). Scheme 110

Note. Before using this chart, check for manifold vacuum to EGR solenoid. Also check hoses for leaks or restrictions,should be at least 7" Hg vacuum at 2000 RPM.

Flow Chart, Code 32: EGR System Failure (1988, All Models). Scheme 111

CODE 33 - MAP SENSOR SIGNAL VOLTAGE HIGH

The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). ECM receives this information as a signal voltage that varies from about 1-1.5 volts at idle to 4-4.5 volts at wide open throttle. If the MAP sensor fails, the ECM will substitute a fixed MAP value and use the TPS to control fuel delivery.

Code 33 will set when signal reading is too high for longer than 5 seconds, when TPS voltage indicates throttle is closed and vehicle speed is zero. Engine misfire or a low/unstable idle may set Code 33. Disconnect MAP sensor and system will go into back-up mode.

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

1. Code 33 will set when the following conditions occur: Signal is too high, for a time of more than 5 seconds. TPS is less than 4%. Engine misfire or a low unstable idle may set Code 33. Disconnect MAP sensor and system will go into back-up mode.
2. If the ECM recognizes the low MAP signal, ECM and wiring are okay.

An open in circuit No. 455 or the connection will result in a Code 33. With ignition on and engine off, voltages should be within the values shown in the table on the test chart.

Code 33 Schematic: MAP Sensor Signal Voltage High. Scheme 112

Flow Chart, Code 33: MAP Sensor Signal Voltage High. Scheme 113

Flow Chart, Code 33: MAP Sensor Signal Voltage High. Scheme 114

CODE 34 - MAP SENSOR SIGNAL VOLTAGE LOW (HIGH VACUUM)

The Manifold Absolute Pressure sensor (MAP) responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage that will vary from about 1-1.5 volts at idle to 4-4.5 volts at wide open throttle. If MAP sensor fails, the ECM will substitute a fixed MAP value and use the TPS to control fuel delivery. Code 34 will sets signal is low and ignition is turned on.

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

1. Code 34 will set when the following conditions occur: Signal is too low and engine is running at less than 1200 RPM. Engine running faster than 1200 RPM. Throttle position more than 21% (over 1.5 volts).
2. If the ECM recognizes the high MAP signal, the ECM and wiring are okay.
3. The "SCAN" tester may not display 12 volts. The important thing is that the ECM recognizes the voltage as more than 4 volts, indicating that the ECM and circuit No. 432 are okay.

An intermittent open in circuit No. 432 or 416 will result in a Code 34. With ignition and engine off, voltages should be within the values shown on the test chart.

Flow Chart, Code 34: MAP Sensor Signal Voltage Low. Scheme 115

Flow Chart, Code 34: MAP Sensor Signal Voltage Low. Scheme 116

CODE 42 - ELECTRONIC SPARK TIMING (EST)

When the system is running on the ignition module, that is, 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 the ECM sees a voltage signal, it sets Code 42 and will not go into the EST mode.

When the RPM for ESTR is reached (about 400 RPM), and by-pass voltage is applied, the EST should no longer be grounded in the ignition module so the EST voltage should be varying.

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. A 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 part through the ignition module. An EST circuit No. 423 shorted to ground will also read less than 500 ohms, however, 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 10-20,000 ohms position will indicate above 5000 ohms. The important thing is that the module is "switched".
4. The module did not switch and this test checks for the following conditions: EST circuit No. 423 shorted to ground. By-pass circuit No. 424 open. Faulty ignition module connection or module.
5. Confirms that Code 42 is a faulty ECM unit and not as intermittent in circuits No. 423 or 424.

If a Code 42 was stored and hard start problem occurs, the problem is most likely a grounded EST line (circuit No. 423). The "SCAN" tester does not have any ability to help diagnose a Code 42 problem. A PROM not fully seated in the ECM can result in a Code 42.

Code 42 Schematic: Electronic Spark Timing ("B"/"G" Bodies). Scheme 117

Code 42 Schematic: Electronic Spark Timing ("F" Body). Scheme 118

Flow Chart, Code 42: Electronic Spark Timing (EST). Scheme 119

Flow Chart, Code 42: Electronic Spark Timing (EST). Scheme 120

CODE 43 - ELECTRONIC SPARK CONTROL (ESC)

Electronic spark control is accomplished with a module that sends a voltage signal to the ECM. As the knock sensor detects engine knock, the voltage from the ESC module to the ECM drops, and this signals the ECM to retard timing. The ECM will retard the timing when knock is detected and RPM is above 900 RPM.

A Code 43 means the ECM has low voltage at circuit No. 485 terminal "B7" for longer than 5 seconds with the engine running or the system has failed the functional check.

This system performs a functional check once engine is started up to check the ESC system. To perform this test the ECM will advance the spark when coolant is above 194°F (95°C) and at a high load condition (near WOT). The ECM then checks the signal at circuit No. B7 to see if a knock is detected. The functional check is performed once per start up and if knock is detected when coolant is below 194°F (95°C), the test has passed and the functional check will not be run. If the functional check fails, the "SERVICE ENGINE SOON" light will remain on until ignition is turned off or until a knock signal is detected.

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

1. If the conditions for a Code 43 are present the "SCAN" tester will always display "YES". There should not be a knock at idle unless an internal engine problem or a system problem exists.
2. This test will determine if the system is functioning. Usually a knock signal can be generated by tapping on the right exhaust manifold. If no knock signal is generated try tapping on block close to the area of the sensor.
3. Because Code 43 sets when the signal voltage on circuit No. 485 remains low, this test should cause the signal on circuit No. 485 to go high. If the ECM unit and wiring are okay, the 12-volt signal should be seen by the ECM as "no knock".
4. This test will determine if the knock signal is being detected in circuit No. 496 or if the ESC module is at fault.
5. If circuit No. 496 is routed too close to secondary ignition wires, the ESC module may mistake the interference as a knock signal.
6. This checks the ground circuit to the module. An open ground will cause the voltage on circuit No. 485 to be about 12 volts which would cause Code 43 functional test to fail.
7. Applying 12 volts to circuit No. 496 with a test light should generate a knock signal. This will determine if the ESC module is operating correctly.

A Code 43 can be caused by a faulty connection at the knock sensor at the ESC module or at the ECM. Also check circuit No. 485 for possible open or short to ground.

Code 43 Schematic: Electronic Spark Control (ESC). Scheme 121

Flow Chart, Code 43: Electronic Spark Control (ESC). Scheme 122

Flow Chart, Code 43: Electronic Spark Control (ESC). Scheme 123

CODE 44 - LEAN EXHAUST INDICATION

The ECM supplies a voltage of about .45 volt between circuits No. 412 and 413 (terminals D7 and D6). The oxygen sensor varies the voltage from one volt (rich exhaust) to .1 volt (lean exhaust). The sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is below 600°F (316°C). An open sensor circuit or cold sensor causes open loop operation. A Code 44 is set when oxygen sensor signal at ECM is below .2 volts for one minute or more, or if time since engine start is one minute or longer.

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

1. A Code 44 is set when the oxygen sensor signal voltage on circuit No. 412 remains below .2 volt for 50 seconds and the system is operating in "closed loop".

Using the "SCAN" tester, observe the block learn values at different RPM and airflow conditions to determine when Code 44 may have been set. 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 MAP sensor output that causes the ECM to sense a higher than normal vacuum will cause the system to go lean. Disconnect the MAP sensor and if the lean condition is gone, replace the sensor.
4. Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can set a Code 44.
5. Fuel system will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the vehicle at various road speeds and/or loads to confirm a problem.
6. If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor. Vacuum or crankcase leaks can cause a lean condition.
7. If the above are okay, problem is a faulty oxygen sensor.

Flow Chart, Code 44: Lean Exhaust Indication. Scheme 124

Flow Chart, Code 44: Lean Exhaust Indication. Scheme 125

CODE 45 - RICH EXHAUST INDICATION

The ECM supplies a voltage of about .45 volts between terminals "D6" and "D7". If measured with a 10-megohms digital voltmeter, this may read as low as .32 volts. The O2 sensor varies the voltage within a range of about one volt if the exhaust is rich, down through about .10 volts if exhaust is lean. The sensor is like an open circuit and produces no voltage when it is below 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. A Code 45 is set when the oxygen sensor signal voltage or circuit No. 412, remains above .7 volt for 50 seconds and in "closed loop". Engine time after start is one minute or more. Throttle angle greater than 2% (about .2 volts above idle voltage) but less than 25%.

Using the "SCAN" tester, observe the block learn values at different RPM conditions, if a Code 45 exists. The block learn values will be around 115.

1. Fuel system will go rich if pressure its too high. The ECM can compensate for some increase. However, if it gets too high, a Code 45 may be set.
2. Check fuel for contaminated oil.
3. An open ground circuit No. 453 (ignition system reference low) may result in EMI, or induced electrical "noise". The ECM looks at this "noise" as reference pulses. The additional pulses result in a higher than actual engine speed signal. The ECM then delivers too much fuel, causing system to go rich. Engine tachometer will also show higher than actual engine speed, which can help in diagnosing this problem.
4. Check for fuel saturation. If full of fuel, check canister control and hoses.
5. An output that causes the ECM to sense a lower than normal vacuum can cause the system to go rich. Disconnecting the MAP sensor will allow the ECM to set a fixed value for the sensor. Substitute a different MAP sensor if the rich condition is gone while the sensor is disconnected.
6. An intermittent TPS output will cause the system to go rich, due to a false indication of the engine accelerating.

Flow Chart, Code 45: Rich Exhaust Indication. Scheme 126

Flow Chart, Code 45: Rich Exhaust Indication. Scheme 127

CODE 51 - FAULTY PROM

Check that all pins are fully inserted in the socket. If okay, replace PROM, clear memory and recheck system. If Code 51 reappears, replace ECM.

CODE 52 - FUEL "CALPAK" MISSING

Install missing or faulty CALPAK.

CODE 54 - FUEL PUMP CIRCUIT LOW VOLTAGE

When the ignition switch is turned on, the ECM will activate the fuel pump relay and run the in-tank fuel pump. The fuel pump will operate as long as the engine is cranking or running, and the ECM is receiving ignition reference pulses. If there are no reference pulses, the ECM will shut off the fuel pump within 2 seconds after ignition is on. Should the fuel pump relay, or the 12-volt relay drive from the ECM fail, the fuel pump will be run through an oil pressure switch back-up circuit.

An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold or engine oil pressure is low. The extended crank period is caused by the time necessary for oil pressure to build enough to close the oil pressure switch and turn on the fuel pump.

Flow Chart, Code 54: Fuel Pump Circuit Low Voltage. Scheme 128

Flow Chart, Code 54: Fuel Pump Circuit Low Voltage. Scheme 129

CODE 55 - FAULTY ECM

Replace ECM unit. Clear codes and confirm "closed loop" operation and no "SERVICE ENGINE SOON" light.

RESTRICTED EXHAUST CHECK 1 (ALL WITH AIR OR PULSAIR)

Note. Proper diagnosis of restricted exhaust system is essential before any components are replaced.

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

1. Remove the rubber hose from the exhaust manifold AIR pipe check valve.
2. Connect fuel pump pressure gauge to hose and nipple from Propane Enrichment Device (J26911).
3. Insert nipple into exhaust manifold AIR pipe.
4. With engine at normal operating temperature and running at 2500 RPM, observe exhaust system backpressure on gauge.
5. If backpressure exceeds 2 3/4 psi, a restricted exhaust system is indicated.
6. Inspect entire system for collapsed pipe, heat stress or possible internal muffler failure.
7. If there is no obvious reasons for excessive backpressure, a restricted catalytic converter should be suspected and replaced.

RESTRICTED EXHAUST CHECK 2 (ALL WITHOUT AIR OR PULSAIR)

1. With engine at normal operating temperature, connect a vacuum gauge to any convenient vacuum port in intake manifold.
2. Disconnect EGR solenoid electrical connector or connect EGR valve directly to vacuum source, by-passing any switches or solenoids.
3. Run engine at 1000 RPM and record vacuum reading.
4. Increase RPM slowly to 2500 RPM and note vacuum reading.
5. If vacuum reading at 2500 RPM decreases more than 3 in. Hg from reading at 1000 RPM, inspect exhaust system for restrictions.
6. Disconnect exhaust pipe from engine and repeat steps 3) and 4). If vacuum reading still drops more than 3 in. Hg with exhaust disconnected, check valve timing.

CHART C1 - ECM REPLACEMENT CHECK CHART

In order to reduce incidents of repeat ECM failure, a revised ECM diagnostic procedure is available. Beginning in 1982, most ECMs are equipped with Integrated Circuits (IC) in place of separate transistors to operate various controlled components.

These ICs, called Quad-Drivers (QDR), have 4 separate outputs, meaning that each QDR can operate up to 4 different components. An inoperative QDR can result in ECM output becoming open or shorted to ground. Often, all 4 outputs of a QDR will fail, even if just one QDR circuit is faulty.

Refer to the following tables to determine which ECMs contain QDRs. Since this procedure is not applicable to ECMs which do not contain QDRs, those ECMs are not listed.

Performing the diagnostic flow chart will identify an inoperative QDR. Once the circuit is identified, it must be repaired to eliminate repeat ECM failure. This diagnostic procedure must be used when "Replace ECM" is the conclusion of any procedure.

ECM QDR IDENTIFICATION (TBI/PFI)

ECM QDR IDENTIFICATION (CARBURETED)

ECM QDR IDENTIFICATION (PFI)

ECM QDR IDENTIFICATION (TBI)

ECM QDR IDENTIFICATION (TBI)

Scheme 130

CHART C1A - PARK/NEUTRAL SWITCH DIAGNOSIS (AUTO TRANS.)

The park/neutral switch is closed to ground in park or neutral, and open in drive ranges. The ECM supplies 12 volts through an internal resistor to circuit No. 434 and senses that switch is closed when voltage at terminal B10 drops to less than one volt.

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

1. Checks for a closed switch to ground in park position. Different makes of "SCAN" tester will read P/N differently. Refer to "SCAN" tester operations manual for type of display used.
2. Checks for an open switch in drive range.
3. Be sure "SCAN" tester indicates drive, even while wiggling shifter to test for an intermittent or misadjusted switch in drive range.

Flow Chart C1A, Park/Neutral Switch Diagnosis (Auto. Trans.). Scheme 131

Flow Chart C1A, Park/Neutral Switch Diagnosis (Auto. Trans.). Scheme 132

CHART C1B - CRANK SIGNAL

Crank signal is a 12-volt signal to ECM during cranking to allow enrichment and cancel diagnostics until engine is running or 12 volt is no longer on circuit.

1. Checks for normal (cranking) voltage to terminal C9 of ECM. Test light should be on during cranking.
2. Determines if source of blown fuse was a faulty ECM.

Flow Chart C1B, Crank Signal. Scheme 133

Flow Chart C1B, Crank Signal. Scheme 134

CHART C1D - MAP OUTPUT CHECK

The MAP measures manifold pressure (vacuum) and sends that signal to ECM. ECM uses this information for fuel and spark control.

1. Checks MAP sensor output voltage to ECM. This voltage, without engine running, represents a barometer reading to ECM.
2. Applying 10 in. Hg (34 kPa) vacuum to MAP sensor should cause voltage to be 1.2 volts less than voltage at step 1). Upon applying vacuum to sensor, change in voltage should be instantaneous. A slow voltage change indicates a faulty sensor.
3. Check vacuum hose to sensor for leaking or restriction. Be sure no other vacuum devices are connected to MAP hose.

Flow Chart C1D, MAP Output Check. Scheme 135

Flow Chart C1D, MAP Output Check. Scheme 136

CHART C2C - IDLE AIR CONTROL

The ECM controls idle RPM with the IAC valve. To increase idle RPM, the ECM moves the IAC valve out, allowing more air to pass by throttle plate. To decrease RPM, it moves the IAC valve in, reducing airflow by the throttle plate. A "SCAN" tester will read the ECM commands to the IAC valve in counts. The higher the count, the more air allowed (higher idle). The lower the count, the less air allowed (lower idle).

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 "0" counts. Occasionally, an erratic or unstable idle may occur. Engine speed may vary 200 RPM, or more, up and down. Disconnect IAC. If the condition is unchanged, the IAC is not at fault.
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. A "SCAN" tester will display 100 or more counts. When performing this test, immediately note RPM on start up, on warm engine, the RPM will decrease rapidly.
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. The "SCAN" tester counts will be above 60 counts, if too low, and "0" counts, if too high.

If idle is too high, stop engine. Turn ignition on and ground diagnostic cable. Wait 30 seconds for IAC to seat then disconnect IAC. Unground diagnostic terminal and start engine. If idle speed is above 450 RPM in drive, locate and correct vacuum leak. If RPM is less than 450 RPM, adjust minimum idle speed or correct other conditions, which may affect idle.

1. Idle speed may be too high or too low. Engine speed may vary up and down, disconnecting IAC does not help. This may set Code 44. A "SCAN" tester and/or voltmeter will read an oxygen sensor output less than .3 volts. Check for low regulated fuel pressure or water in fuel. A lean exhaust, with an oxygen sensor output fixed above .8 volts, will be a contaminated sensor. This may also set Code 45.
2. Idle speed too low. If "SCAN" tester counts are above 80, system obviously rich and may exhibit Black smoke from the exhaust. The "SCAN" tester and/or voltmeter will read an oxygen sensor signal fixed above .8 volts. Check for high fuel pressure and/or injector leaking or sticking.
3. Remove IAC and inspect bore for foreign material or evidence of IAC valve dragging in the bore.

Flow Chart C2C, Idle Air Control (IAC). Scheme 137

Flow Chart C2C, Idle Air Control (IAC). Scheme 138

CHART C3 - CANISTER PURGE CHECK

Canister purge is controlled by a solenoid that allows manifold vacuum to purge canister when de-energized. The ECM supplies a ground to energize solenoid (purge off). If diagnostic test terminal is grounded with engine stopped with engine running, purge solenoid is de-energized (purge on).

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

1. Checks to see if the solenoid is opened or closed. The solenoid is, normally energized in this test, so it should be closed.
2. Checks for a complete circuit. Normally, there is battery voltage on circuit No. 39, and the ECM provides a ground on circuit No. 428. A shorted solenoid could cause an open circuit in the ECM.
3. Completes functional check, by grounding test terminal. Normally this should de-energize the solenoid and allow the vacuum to drop (purge "ON").
4. Solenoids, or relays, are turned on or off by the ECM internal electronic switches, called "Drivers". Each driver is part of a group of 4 called "Quad-Drivers". Failure of one can damage any other driver within the set. Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure of the ECM "Driver". Using an ohmmeter, check solenoid coil resistance of all ECM controlled solenoids and relays before installing a replacement ECM.

Flow Chart C3, Canister Purge Check. Scheme 139

Note. This chart only covers the solenoid portion of the Canister Control Purge system. To test the control valve(s), see diagnosis under general description.

Flow Chart C3, Canister Purge Check. Scheme 140

CHART C4B - IGNITION SYSTEM CHECK

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

1. Two wires are checked, to ensure that an open is not present in a spark plug wire. If spark occurs with EST connector disconnected, pick-up coil output is too low for EST operation.
2. A spark indicates the problem must be the distributor cap or the rotor.
3. Normally, there should be battery voltage at the "C" and "plus" terminals. Low voltage would indicate an open or a high resistance circuit from the distributor to the coil or ignition switch. If "C" terminal voltage was low, but "plus" terminal voltage is 10 volts or more, circuit from "C" terminal to ignition coil or ignition coil primary winding is open.
4. Checks for a shorted module or grounded circuit from the ignition coil to the module. The distributor module should be turned off, so normal voltage should be about 12 volts. If the module is turned on, the voltage would be low, but above one volt. This could cause the ignition coil to fail from excessive heat. With an open ignition coil primary winding, a small amount of voltage will leak through the module from the battery to the tachometer terminal.
5. Applying 1.5-8 volts to module terminal "P" should turn the module on. The tachometer terminal voltage should drop to about 7-9 volts. This test will determine whether the module or coil is faulty or if the pick-up coil is not generating the proper signal to turn the module on. This test can be performed by using a DC battery with a rating of 1.5-8 volts. The use of the test light is mainly to allow the "P" terminal to be probed more easily. Some digital multi-meters can also be used to trigger the module by selecting ohms, usually in the diode position. In this position the meter may have voltage across its terminals which can be used to trigger the module. The voltage in the ohm position can be checked by using a second meter or by checking the manufacturer's specification of the "SCAN" tester being used.
6. This should turn off the module and cause a spark. If no spark occurs, the fault is most likely in the ignition coil because most module problems would have been found before this point in the procedure. A module tester could determine which is a fault.

Flow Chart C4B, Ignition System Check. Scheme 141

Flow Chart C4B, Ignition System Check (1 Of 2). Scheme 142

Flow Chart C4B, Ignition System Check (2 Of 2). Scheme 143

CHART C5 - ELECTRONIC SPARK CONTROL (ESC) CHECK

Electronic Spark Control (ESC) is accomplished with a module that sends a voltage signal to the ECM. As the knock sensor detects engine knock, voltage from the ESC module to the ECM is shut off. This signals the ECM to retard timing, if engine speed is over 900 RPM.

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

1. If a Code 43 is not set, but a knock signal is indicated while running at 1500 RPM, listen for an internal engine noise. Under a no load condition, there should not be any detonation, and if knock is indicated, an internal engine problem may exist.
2. Usually a knock signal can be generated by tapping on the right exhaust manifold. This test can also be performed at idle. Test No. 1 was run at 1500 RPM, to determine if a constant knock signal was present, which would affect engine performance.
3. This will test whether the knock signal is due to the sensor, a basic engine problem, or the ESC module.
4. If the module ground circuit is faulty, the ESC module will not function correctly. The test light should light indicating the ground circuit is okay.
5. Using a test light with 12 volts at circuit No. 496 should generate a knock signal to determine whether the knock sensor is faulty, or the ESC module can't recognize a knock signal.

Flow Chart C5, Electronic Spark Control (ESC) Check. Scheme 144

Flow Chart C5, Electronic Spark Control (ESC) Check. Scheme 145

CHART C6B - AIR MANAGEMENT CHECK (PEDES VALVE)

Air management is controlled by a port valve and a converter valve, each with an ECM controlled vacuum solenoid. When solenoid is grounded by ECM, air pressure will activate valve and allow pump air to be directed either to the solenoid that is grounded or port solenoid that may be also grounded.

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

1. This is a system functional check. Air is directed to ports during "open loop" and all engine starts are in open loop (even on a warm engine). Since the air to the ports time is very short on some engines, prepare to observe port air prior to engine start up. On some engines, this can be done by squeezing a hose. On others, steel pipes have to be disconnected.
2. This should normally set a Code 22. When any code is set, the ECM opens the ground to the air control valve and allows air to divert. This checks for ECM response to a fault that may exist. A ground in the control valve circuit to the ECM would prevent diverter action.
3. This checks for a ground circuit to the ECM. If test light is off, this is normal and would indicate the circuits are not grounded.
4. Checks for an open in the solenoid control circuits. Grounding the test terminal should ground both solenoid circuits. Normally, the test light should be on which indicates the problem is not in the ECM or wiring but at the solenoid connections or the switching valve itself.
5. Checks for a grounded switching valve circuit. If test light is off, this would indicate the circuit is normal and fault is in the switching valve.

Flow Chart C6B, Air Management Check (Pedes Valve). Scheme 146

Flow Chart C6B, Air Management Check (Pedes Valve, 1 Of 2). Scheme 147

Flow Chart C6B, Air Management Check (Pedes Valve, 2 Of 2). Scheme 148

CHART C7 - EGR CHECK

The ECM operates a solenoid to control the EGR valve. This solenoid is normally closed. By providing a ground path, the ECM energizes the solenoid which then allows vacuum to pass to the EGR valve. The ECM control of the EGR is based on the following inputs

1. Engine coolant temperature above 25°C.
2. TPS idle.
3. MAP.

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

1. Checks for a stuck open solenoid.
2. Checks for solenoid always being energized.
3. Grounding test terminal should energize solenoid and vacuum should drop.
4. Negative backpressure valve should hold vacuum with the engine off.
5. When the engine is started, exhaust backpressure should cause vacuum to bleed off and valve to fully close.

Flow Chart C7, EGR Check. Scheme 149

Flow Chart C7, EGR Check. Scheme 150

200-4R TORQUE CONVERTER CLUTCH (TCC) DIAGNOSIS (1 OF 2)

The purpose of automatic transmission torque converter clutch feature is to eliminate power loss of torque converter stage when vehicle is in cruise condition. This allows convenience of automatic transmission and fuel economy of a manual transmission. Fused battery ignition is supplied to TCC solenoid through brake switch. The ECM will engage TCC by grounding circuit No. 422 to energize the solenoid. TCC engages when vehicle speed is above 24 MPH, engine is at normal operating temperature, throttle position sensor output not changing (indicating steady road speed), and/or brake switch is closed.

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

1. Confirms 12-volt supply as well as continuity of TCC circuit.
2. Grounding the diagnostic terminal with engine off, should energize the capability of the ECM to control the solenoid
3. Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure to the ECM "driver". Using an ohmmeter, check the solenoid coil resistance of all ECM controlled solenoids and relays before installing a replacement ECM. Replace any solenoid or relay that measures less than 20 ohms.

An engine coolant temperature coolant thermostat that is stuck open or opens at too low a temperature, may result in an inoperative TCC. If TCC engages before "SCAN" indicates solenoid or sump over temperature switch may be faulty.

Flow Chart C8A, 200-4R TCC Electrical Diagnosis. Scheme 151

Using A "Scan" Tool, Check The Following And Correct If Necessary

1. Coolant Temperature Should Be Above 65°C
2. TPS - Be Sure TPS Signal Is Not Erratic
3. VSS - Be Sure "Scan" Displays VSS With Drive Wheels Turning, If Code 24 Is Present, See Code Chart 24

Flow Chart C8A, 200-4R TCC Electrical Diagnosis. Scheme 152

200-4R TORQUE CONVERTER CLUTCH (TCC) DIAGNOSIS (2 OF 2)

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

1. Unless switch or circuit No. 446 is open, the "SCAN" tester should display "NO", indicating the transmission is not in 4th gear. The 4th gear switch should only be open while in 4th gear.
2. This test determines if the ECM and wiring are okay. Grounding circuit No. 446 should cause the "SCAN" to display "NO", indicating the transmission is not in 4th gear.
3. Checks operation of the 4th gear switch. When the transmission shifts into 4th gear the switch should open and the "SCAN" should display "YES".
4. Disconnecting the TCC connector simulates an open switch to determine if circuit No. 446 is shorted to ground or the problem is in the transmission.

A road test may be necessary to verify customer complaint. If the "SCAN" tester indicates TCC is turning "ON" and "OFF" erratically, check the state of the 4th gear switch to be sure it is not changing states under a steady throttle position. If the switch is changing, check connections and wire routing carefully. Also if 4th gear switch is always open, the TCC may engage as soon as sufficient oil pressure is reached.

Flow Chart C8A (2 Of 2), TCC Electrical Diagnosis. Scheme 153

Note. Checks made in this chart will not prevent the TCC from working, but will affect engagement or disengagement points.

Flow Chart C8A (2 Of 2), TCC Electrical Diagnosis. Scheme 154

5.0L TBI Component Locations ("F" Body). Scheme 155

5.0L TBI ECM Terminal ID & Pin Voltages ("F" Body). Scheme 156

5.0L TBI CCC Wiring Diagram (1988 "F" Body). Scheme 157