Feedback Carburetor Tests W/codes Buick Electra Estate Wagon

MODEL IDENTIFICATION

Repair procedures in this article are identified by body type. The following table lists GM division, model name, and body type.

MODEL IDENTIFICATION

DESCRIPTION

Note. Most Computer Command Control (CCC) problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoses. Before considering the CCC 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.

The Computer Command Control (CCC) system used on the 1985 General Motors vehicles monitors as many as 19 engine/vehicle functions. This system controls engine operation and lowers exhaust emissions while maintaining good fuel economy and driveability. The Electronic Control Module (ECM) is the "brain" of the CCC system. The ECM controls as many as 12 engine related systems constantly adjusting engine operation.

The CCC 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 catalytic converter can control oxides of nitrogen (NOx), hydrocarbon (HC) and carbon monoxide (CO) emissions.

ECM Systems Controlled (Outputs)

1. A/C
2. Air Management
3. Canister Purge
4. Diagnostics
5. Check Eng. Light
6. Data Output (ALCL)
7. Diagnostic Test Terminal (ALCL)
8. Early Fuel Evaporation (EFE)
9. Electric Fuel Pump
10. Electronic Fuel Inj. (TBI & Port)
11. Electronic Spark Control (ESC)
12. Electronic Spark Timing (EST)
13. Engine Cooling Fan
14. Exhaust Gas Recirculation (EGR)
15. Fuel Control (M/C solenoid)
16. Hood Louvre
17. Idle Air Control (IAC)
18. Idle Speed (ISC. ILC ISS)
19. Transmission Converter Clutch (TCC)
20. Turbo Wastegate

ECM Operating Conditions Sensed (Inputs)

1. A/C "ON" or "OFF"
2. Engine Coolant Temperature
3. Ambient Temperature
4. Barometric Press. (BARO)
5. Brake "ON" or "OFF"
6. Cruise Control "ON" or "OFF"
7. Differential Press. (Eng. Vacuum)
8. Distributor Reference
9. Crankshaft Position
10. Engine Speed
11. EGR Vacuum
12. Engine Cranking
13. Engine Detonation (ESC)
14. Exhaust Oxygen (O2)
15. Manifold Absolute Press. (MAP)
16. Mass AirFlow (MAF)
17. Manifold Air Temperature (MAF)
18. Park/Neutral Sw. Position (P/N)
19. System Voltage
20. Throttle Position (TPS)
21. Transmission Gear Position
22. Vehicle Speed (VSS)

Schematic of Computer Command Control System. Scheme 68

Sectional View of Mixture Control Solenoid. Note air bleed above main metering rod. Scheme 69

DIAGNOSTIC SYSTEM OPERATION

Note. A "CHECK ENGINE" lamp driver is installed in the wiring harness from ECM to the "CHECK ENGINE" lamp. This driver amplifies the power to the "CHECK ENGINE" lamp to reduce amperage draw on the battery.

The ECM of the CCC system is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, the ECM will light the Amber "CHECK ENGINE" lamp located on the instrument panel. When the malfunction is detected and the lamp is turned on, a corresponding trouble code will be stored in the ECM memory. Malfunctions are recorded as "hard failures" or as "intermittent failures".

1. "Hard failures" cause the "CHECK ENGINE" lamp to glow and remain on until the malfunction is repaired. If the "CHECK ENGINE" lamp comes on and remains on during vehicle operation, the cause of the malfunction must be determined.
2. "Intermittent failures" cause the "CHECK ENGINE" lamp to flicker or go out after about 10 seconds when the fault goes away. However, the corresponding trouble code will be retained in the ECM memory. "Intermittent failures" may be sensor related. If a sensor fails, the ECM will use a substitute value in its calculations to continue engine operation. In this condition, service is not mandatory; but loss of good driveability may be encountered. If the related fault does not reoccur within 50 engine restarts, the related trouble code will be erased from the ECM memory.

As a bulb and system check, the "CHECK ENGINE" lamp will glow when the ignition switch is turned on and the engine is not running. When the engine is started, the lamp should go out. If not, a malfunction has been detected in the CCC system.

Note. Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others require operation for 5 minutes or longer.

BASIC DIAGNOSTIC PROCEDURE

Diagnosis of the CCC system should be performed in the following order

1. Make sure that all engine systems not related to the CCC system are operating properly. Do not proceed with testing unless all other problems have been repaired.
2. Put the system into diagnostic mode and record trouble codes flashed by "CHECK ENGINE" light. Exit the diagnostic mode.
3. If trouble codes were displayed, decide whether the codes are "hard" or "intermittent" trouble codes.
4. Proceed to Diagnostic Circuit Check chart. Follow all instructions given in that chart.
5. If no trouble codes were displayed, proceed to System Performance Check for carbureted models, or Field Service Mode for fuel injection models.
6. If no trouble is indicted by any of these charts, use the TROUBLE SHOOTING material in the CCC TESTS W/O CODES article in this section. The comments there will send you to the proper component charts or tell you what to fix.
7. After any repairs are made, perform System Performance Check. Clear any trouble codes.

Note. Each of the steps listed here are described later in this section. If you are unsure of the proper way to test, read through the following material.

Scheme 70

1. Turn ignition switch on but do not start engine. "CHECK ENGINE" light should glow. Locate assembly line data link (ALDL) connector attached to ECM wiring harness under instrument panel. Insert spade lug terminal across "TEST" terminal and "GROUND" terminal. (Scheme 70) CAUTION: Inserting spade lug in terminals of ALDL connector grounds "TEST" terminal lead. Do not ground ALDL connector until after ignition is on or engine is started. (Scheme 70): ALDL Connector Terminal Locations
2. "CHECK ENGINE" 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, then if any trouble codes are stored in the ECM memory, they will be displayed in the same manner.
3. Trouble codes will be displayed from lowest to highest numbered codes (3 times each) and be repeated as long as the "TEST" terminal of the ALDL connector is grounded.
4. To exit diagnostic mode, turn ignition switch off and remove spade lug terminal from ALDL connector.

CLEARING TROUBLE CODES

Turn ignition switch on and ground "TEST" lead at ALDL connector. Turn ignition switch off and remove ECM fuse from fuse block for 10 seconds. Remove "TEST" lead ground.

READING TROUBLE CODES

The ECM stores component failure information for CCC system under a related trouble code which can be recalled for diagnosis and repair. When recalled, these codes will be displayed by flashes of the "CHECK ENGINE" light. Trouble codes are displayed starting with the lowest numbered code. Only codes that represent a definite malfunction will be shown.

Note. Chevette and 1000 models (Minimum Function system) do not have "long-term" memory capability. Codes in the memory will be erased when ignition switch is turned off. Diagnostic ability exists only while engine is running and malfunction exists.

Trouble codes are read by counting flashes of the "CHECK ENGINE" light, or by reading the output of a diagnostic tool connected to the ALDL connector under the dashboard. The tool is faster and more accurate, but is not mandatory.

If the tool is not available, read the flashes of the dashboard light. 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.

Note. On EFI models only, "CHECK ENGINE" light will indicate operational mode of engine. In closed loop, the "CHECK ENGINE" light will flash at a rate of 1 flash per second. In open loop, the "CHECK ENGINE" light will flash at a rate of 2.5 flashes per second.

TROUBLE CODE COMPONENT IDENTIFICATION

ECM TROUBLE CODE IDENTIFICATION

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 failure" codes. To determine "hard failure" codes and "intermittent failure" codes, proceed as follows

1. 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 and start engine. "CHECK ENGINE" light should go out. Run warm engine at specified curb idle for 2 minutes and note "CHECK ENGINE" light.
3. If "CHECK ENGINE" 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. NOTE: Anytime codes "51", "52", "54" or "55" are displayed with another code, start with "50-series" code first, then proceed to lowest numbered code.
4. If "CHECK ENGINE" light does not come on, all stored trouble codes were "intermittent failures". Exceptions are noted under Diagnostic Procedure.

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 fix a problem when the On-Car Diagnostics don't work.
2. Charts where a stored trouble code leads you to a particular problem.
3. Charts which are used because the System Performance Check (carbureted engines) or the Field Service Mode (EFI engines) found a problem.
4. "Engine Cranks But Won't Run" charts.

DIAGNOSTIC CIRCUIT CHECK

1. If complaint is "CHECK ENGINE" lamp related, this check will lead to the most likely problem area, if a malfunction exists. Enter diagnostic mode and record stored trouble codes. Begin diagnosis with the lowest numbered code shown and go to the numbered trouble code chart.
2. If code "51" is displayed, see PROM removal and installation in this article. If codes "54" or "55" are displayed with another code, always refer to diagnostic chart for code "54" or "55" first, then proceed to next lowest numbered code.

DIAGNOSTIC SYMPTOM CHECK

1. If complaint is not "CHECK ENGINE" lamp related, this check will lead to most likely problem area. However, first make checks that would normally be made for the complaint on a vehicle without CCC system.
2. Follow instructions in diagnostic chart and repair malfunction. After repair, perform System Performance Check (carbureted models) or Field Service Mode Check (EFI models).

SYSTEM PERFORMANCE CHECK (CARBURETED MODELS ONLY)

1. This check verifies that CCC system is functioning correctly. This check should always be made after any repair on CCC system.
2. When performing this check, always engage parking brake and block DRIVE wheels. Parking brake on front-wheel drive models does not hold drive wheels. On engines equipped with Varajet carburetors (E2SE Model), remove bowl vent line at carburetor and plug hose at carburetor during check and reconnect it after the check is complete.
3. On some engines, the 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.

FIELD SERVICE MODE CHECK (EFI MODELS ONLY)

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

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

DIAGNOSTIC TOOLS

The CCC system does not require special tools for diagnosis. A tachometer, a dwell meter, test light, ohmmeter, digital voltmeter with 10 megohms impedance (minimum), vacuum pump, vacuum gauge and 6 jumper wires 6" long (1 wire with female connectors at both ends; 1 wire with male connector at both ends; 4 wires with male and female connectors at opposite ends) are the only tools necessary for diagnosis.

Note. Special testers can be used to read trouble codes and check voltages in the system. These tools can save a great deal of time, but are not required. Refer to tester manual for operating procedures.

A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.

On carbureted models, the dwell meter is used to measure the time the M/C solenoid is on or off. This indicates if the M/C solenoid is working and the fuel mixture strength (rich or lean). The dwell meter is set on the 6-cylinder scale regardless of the number of cylinders in the engine.

Dwell meter is connected to Green connector located near the carburetor. This connector will not be connected to any circuit EXCEPT when you are testing with the dwell meter. DO NOT allow terminal wire to come in contact with any ground source, including rubber hoses.

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

If engine is at operating temperature and idling, dwell meter needle should be varying between 10-50°. This indicates closed loop operation. If needle does not move, open loop operation is indicated.

Diagnostic Circuit Check determines if: 1) the "CHECK ENGINE" light works, 2) the ECM is operating and can recognize a fault, and 3) any codes are stored. It also checks to see if stored codes indicate an intermittent problem. This is the starting point for any diagnosis. If no codes are indicated, go to the System Performance Check. If no additional checks are called out from the System Performance Check, go to the Driveability Symptoms.

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

1. Check operation of the "CHECK ENGINE" light. Key "ON", engine not running, light should be on steady.
2. Grounding test terminal will flash a Code 12 and any stored trouble codes. The light must go "ON" and "OFF" to indicate a code. The light going from "Bright" to "Dim" is not considered a code. See CHART A6.
3. This step will determine if any codes, other than Code12, are still present or were intermittent and are no longer stored. Clear memory. Run vehicle for 2 minutes. See if trouble code(s) reset.
4. If the light is "ON", fault is still present. Go to the applicable trouble code chart.
5. If the light is "OFF", the fault is either intermittent, or it is a code that cannot be set with vehicle stationary. For codes that cannot be set during the Diagnostic Circuit Check, the applicable trouble code chart will determine if those codes are intermittent.

Diagnostic Circuit Check Flow Chart. Scheme 71

Diagnostic Circuit Check Flow Chart. Scheme 72

SYSTEM PERFORMANCE CHECK

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

1. 1) This test checks carburetor ability to change air/fuel mixture. Disconnecting M/C solenoid makes carburetor run full rich, reconnecting it with dwell lead grounded makes carburetor run full lean. RPM normally drops 300-1000 RPM as solenoid is reconnected.
2. 1A) If plugging PCV, Purge, or Bowl Vent hose causes RPM to drop more than 300 RPM, that hose leads to the source of the problem.
3. 2) This test checks for proper control of idle circuit.
4. 2A) This indicates a full rich command to the carburetor, caused by: lean engine condition, grounded O2 sensor wire or bad sensor, open wire from ECM terminal "14" to ground, open wire to ECM terminal "22" or open coolant sensor circuits 410 or 452.
5. 2B) This indicates an open loop condition that can be caused by: an open O2 sensor circuit or bad sensor, an open coolant sensor circuit or an open wire from ECM terminal "14" to ground.
6. 2C) This indicates a full lean command which can be caused by: M/C solenoid wires reversed, leaking Bowl Vent valve, excessive fuel in vapor canister, fuel in crankcase, faulty carburetor calibration or carburetor or silicone contaminated O2 sensor.
7. 2D) Indicates closed loop operation. Normal dwell reading is between 10°-50° but varying. Run engine at 2000 RPM for 1 minute to ensure O2 sensor is warm.
8. 3) Checks for proper control of main metering system. RPM must be at least 3000 to get into the main metering system operation.
9. 3A) A missing "O" ring between the switching valve solenoid and valve, or a defective valve, may cause air to leak into the exhaust ports at higher RPM only.

System Performance Check Flow Chart. Scheme 73

System Performance Check Flow Chart. Scheme 74

CHART A1 - DWELL FIXED UNDER 10°

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

1. 1) This test determines if problem is CCC or engine related. Dwell should start increasing as soon as engine is choked and increase until it is over 50°. If dwell responds, problem is lean engine.
2. 1A) This checks for causes of lean condition that resulted in full rich command.
3. 2) This test checks for ECM response to input to O2 sensor circuit. The voltmeter is used to put a voltage on the O2 sensor circuit to simulate a rich condition. Dwell should increase (a lean command) if ECM and harness are good.
4. 3) This test checks for normal coolant sensor circuit condition. Voltage on a normalized hot engine should be under 2.5 volts.
5. 4) This step checks for an open in the ground circuit to ECM term. "14" and grounded O2 sensor circuit. Terminal "2" voltage should be under 1.0 volt at idle. A high voltage could be caused by an open in the circuit at term. "22". Normally this will cause Codes 21 and 34 (and 35 if equipped with idle speed control) but won't set them on some engines.

Flow Chart A1, Dwell Fixed Under 10°. Scheme 75

Flow Chart A1, Dwell Fixed Under 10 Degrees. Scheme 76

Flow Chart A1, Dwell Fixed Under 10° - Circuit Diagram. Scheme 77

CHART A2 - DWELL FIXED BETWEEN 10°-50°

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

1. 1) Run engine 1 minute to warm O2 sensor. Grounding O2 sensor input checks ECM response to a "lean" signal. Normal response is dwell decreasing to full rich command.
2. 1A) On some ECM's, an open circuit to term. "14" can cause open loop.
3. 1B) Checks output of O2 sensor with full rich command from ECM caused by grounded O2 sensor input. Normal response is voltage at O2 sensor over .8 volt.
4. 2) This step grounds O2 sensor circuit at ECM to check for opens in wiring to ECM terminals "9" and "14". Normal response to "lean" signal is dwell decrease.
5. 3) This step checks for voltage to the coolant sensor. Normal reading on a warm engine is less than 2.5 volts. An open circuit would cause a reading of approximately 5 volts.

Flow Chart A2, Dwell Fixed Between 10°-50°. Scheme 78

Flow Chart A2, Dwell Fixed Between 10-50 Degrees. Scheme 79

CHART A3 - DWELL FIXED OVER 50°

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

1. This test determines whether problem is related to engine or electronics. Normal response is dwell decrease, this indicates that O2 sensor, harness and ECM are okay; problem is a rich engine. NOTE: If engine is very rich, a large air leak may be required to lean mixture. When mixture is lean enough, engine will begin to run rough.
2. If plugging the PCV or bowl vent vacuum hose causes the dwell to decrease, that hose leads to the source of the problem.
3. This checks ECM response to a "lean" O2 signal. Normal response to this test is low dwell. No dwell change means a defective ECM. This test also eliminates the possibility of an open sensor wire. An open wire would cause open loop operation and may set Code 13.
4. This test checks for excessive voltage in O2 line. If under .55 volt, wire and ECM are okay, fault is in O2 sensor. If over .55 volt, wire is shorted to battery voltage or ECM is faulty.

Flow Chart A3, Dwell Fixed Over 50°. Scheme 80

Flow Chart A3, Dwell Fixed Over 50 Degrees. Scheme 81

CHART A5 - "CHECK ENGINE" LIGHT INOPERATIVE

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

1. This checks for blown gauge fuse or open in "CHECK ENGINE" light circuit (including I.P. connector), printed circuit and "CHECK ENGINE" lamp. Normal response is lamp "ON".
2. This test checks for shorted ECM. Grounding ECM term. "G" will turn "CHECK ENGINE" light "OFF". Normal response is lamp "ON".
3. This test checks for grounded wire from term. "C" of lamp driver to term. "G" of ECM, an open circuit to term. "B" of lamp driver, a bad ground or faulty lamp driver. Normal reading is about 9-11 volts.
4. This test checks for open in the wire to term. "B", normal response is approximately battery voltage.
5. This checks for an open wire to term. "E" from the "CHECK ENGINE" lamp. With term. "E" grounded, lamp should normally light.
6. This test checks for a grounded wire from driver term. "C" to ECM term. "G". Normal response is light "ON".

Flow Chart A5, "CHECK ENGINE" Light Inoperative. Scheme 82

Flow Chart A5, "CHECK ENGINE" Light Inoperative. Scheme 83

Chart A5, "CHECK ENGINE" Light Inoperative - Ckt Diagram. Scheme 84

CHART A6 - WON'T FLASH CODE 12

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

1. This step checks for short to battery voltage in wire to term. "C" or faulty lamp driver. Normal reading is 9 to 11 volts.
2. This step checks to see if problem is related to the ECM or lamp driver. Grounding term. "C" should turn lamp "OFF".
3. Grounding term. "G" at ECM and finding light "ON" indicates an open in the wire to term."C" of lamp driver. Grounding term. "G" should turn lamp "OFF".
4. This step checks for open in wire from ECM to test terminal in ALDL connector. The lamp should flash Code 12 when term. "5" is grounded.
5. This checks for proper voltage supply to ECM, both should read over 9 volts. Term. "C" is ignition and term. "R" is constant battery for long term memory.
6. This test checks for bad ground in ECM. Terms. "A" and "U" are connected together in the ECM.
7. This step distinguishes between a faulty ECM and PROM. Normal response is for Code 51 to flash even though the PROM is not installed in the ECM. If no Code 51, ECM is faulty.

Flow Chart A6, Won't Flash Code 12. Scheme 85

Scheme 14: Flow Chart A6, Won't Flash Code 12. Scheme 86

CODE 12 - NO DISTRIBUTOR REFERENCE PULSES

Code 12 means the ECM is "ON" and sees no reference pulse from the distributor. This is a normal code with the ignition "ON" and the engine not running. Code 12 is not stored and will only flash when the fault is present. With engine running, Code 12 could mean an open or ground in distributor reference circuit. Code 41 will appear with Code 12 if engine is running with no distributor reference signal. If problem clears, Code 41 will store.

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

1. This test checks for a poor connection at EST 4-wire connector as being the source of no reference pulse. Check for corrosion, connector terminals not fully seated, or terminal not properly attached to wire. Terminal must be removed from the connector and carefully inspected.
2. This step determines if a reference pulse is being sent to the ECM. Voltage should increase as you go from idle to part throttle. A voltage increase indicates the signal is being generated by the module and fault is a bad connection at the ECM, or faulty ECM. To check the connection at ECM, terminal must be removed from connector.
3. With an open circuit, there is still a small amount of voltage at the ECM. It will not increase when throttle is opened. If circuit from term. "10" to module is not opened or grounded, source of no signal is the module.

Code 12, No Distributor Reference Pulses. Scheme 87

Code 12, No Distributor Reference Pulses. Scheme 88

CODE 13 - OPEN OXYGEN SENSOR CIRCUIT

Code 13 indicates an open in the O2 sensor circuit with the following conditions

1. O2 sensor voltage is within a specified range.
2. Above a specified TPS value.
3. More than specified time after engine has warmed up.

The ECM supplies about .45 volt between terms. "9" and "14". Voltage may read as low as .32 volt when measured with a 10 megohm digital volt-ohm meter. The O2 sensor varies the voltage within a range of about 1 volt (rich exhaust) to about .1 volt (lean exhaust).

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

1. This test checks to see if problem still exists. Fixed dwell indicates fault.
2. By grounding the O2 sensor circuit to the ECM, a "low voltage (lean) signal" is sent to the ECM. This should result in a "full rich (low dwell) command".
3. This test checks O2 sensor. With the rich command, the O2 sensor should read a high voltage, over .8 volt. If the O2 sensor functions, fault is in the connections to the sensor.
4. Checks for an open in the ECM-O2 sensor ground circuit. Normal voltage is below 1 volt if the circuit is complete. The worse the connection is, the higher the voltage will read.
5. This grounds the O2 signal wire at the ECM. Dwell should go to below 10°, since this is a "low voltage signal" indicating lean exhaust. No change indicates a problem at the ECM connections, or a faulty ECM.

Code 13, Open Oxygen Sensor Circuit - Flow Chart. Scheme 89

Code 13, Open Oxygen Sensor Circuit - Flow Chart. Scheme 90

CODE 14 - COOLANT SENSOR SHORTED

Code 14 means the ECM has seen low resistance of the coolant sensor circuit as high engine temperature, or low voltage at ECM terminal "3", for a time longer than specified.

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

1. This test determines whether fault is in sensor or circuit. Normal circuit voltage is about 5 volts. NOTE: Coolant sensor IS NOT connected during this test.
2. Checks for ground between ECM and coolant sensor. Test light to battery positive will be "OFF" in an ungrounded circuit.

Code 14, Coolant Sensor Shorted - Flow Chart. Scheme 91

Code 14, Coolant Sensor Shorted - Flow Chart. Scheme 92

CODE 15 - COOLANT SENSOR OPEN

Code 15 means the ECM has seen the resistance of the Coolant Sensor circuit too high. This could be due to high resistance (cold engine temperature) or high voltage at ECM term. "3", for too long a time. This may cause detonation on a warm engine due to excessive spark advance, or poor driveability due to inaccurate fuel control.

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

1. If problem still exists, "CHECK ENGINE" light will come on and Code 15 will be set.
2. This test checks if fault is coolant sensor or lack of voltage to sensor. Normal reading is 5 volts across coolant sensor connector.
3. This test determines whether the low voltage at the sensor connector is due to opens in the coolant sensor wires, or in another part of the 5 volt reference circuit. Normal voltage is about 5 volts from ECM terms. "3" to "7".
4. This test checks resistance of the coolant sensor. If the resistance is within the chart specifications, coolant sensor is not faulty. Check for corrosion at the connector or low coolant level.

Code 15, Coolant Sensor Open - Flow Chart. Scheme 93

Code 15, Coolant Sensor Open - Flow Chart. Scheme 94

CODE 21 - TPS CIRCUIT HIGH

Code 21 means that the ECM has seen a high TPS voltage for more than about 10 seconds, below a specified RPM or below a specified engine load. Due to the pull-up resistor between terms. "21" and "2" within the ECM, an open in the TPS circuit will place about 5 volts (high TPS signal) at term. "2" of ECM.

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

1. This test checks the circuits from the TPS connector back to the ECM. Both wires should read about 5 volts due to the pull-up resistor in the ECM. NOTE: A 10 Megohm resistance meter must be used. A lower resistance voltmeter would read virtually zero at term. "B".
2. This test checks if low voltage at TPS connector is an open in the circuit or a faulty ECM. A normal reading at the ECM is about 5 volts.
3. This test simulates closed throttle. Dwell should increase if the ECM is good.
4. This tests the resistance of the TPS switch. Normal reading is less than 20,000 ohms.

Code 21, TPS Circuit High - Flow Chart. Scheme 95

Code 21, TPS Circuit High - Flow Chart. Scheme 96

CODE 22 - TPS CIRCUIT LOW (5.0L VIN Y ONLY)

Code 22 indicates the ECM has seen low TPS voltage longer than 20 seconds at terminal "2" of the ECM.

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

1. This test checks for voltage reference at the TPS harness connector. Normal voltage should be about 5 volts.
2. This test separates an electrical circuit problem from a faulty TPS. Normal circuit voltage reading will be about 5 volts.
3. This test checks to see if the low reference voltage is due to a grounded wire pulling a low voltage reference or an open circuit, including the ECM.

Code 22, TPS Circuit Low - Flow Chart (5.0L VIN "Y" Only). Scheme 97

Code 22, TPS Circuit Low - Flow Chart (5.0L VIN "Y" Only). Scheme 98

CODE 23 - M/C SOLENOID CIRCUIT LOW

Code 23 indicates that the ECM has sensed a low steady voltage at ECM term. "18". Normal voltage at term. "18" is rising and falling as the solenoid is turned "ON" and "OFF". This code could be caused by a ground on the ECM side of the M/C solenoid or an open in the M/C solenoid circuit. A grounded circuit will cause a full lean condition and very poor driveability. An open circuit will cause a full rich condition and poor economy, odor, smoky exhaust or poor driveability.

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

1. This checks for a complete circuit from the battery to the M/C solenoid dwell lead. Normal reading should be battery voltage. Battery voltage means there might be an open circuit between dwell connector and ground. No voltage could be either an open between the connector and battery or a ground on the ECM side of the M/C solenoid.
2. This test checks for battery voltage on the pink ignition source wire. Test light should light between the ignition source and ground.
3. This test checks for an open in the solenoid to ECM circuit. Normal circuit will read about battery voltage at Term. "18" of the ECM.
4. This test determines whether fault is in the M/C solenoid, a ground in the circuit to the ECM or the ECM. A light will indicate a ground in circuit to term. "18" or a faulty ECM. NOTE: A test light must be used in this step. A voltmeter may give an inaccurate indication.
5. This test checks for ground in wire to ECM term. "18". If wire is grounded, light will stay "ON".

Code 23, M/C Solenoid Circuit Low - Flow Chart. Scheme 99

NOTE: Check connections at M/C solenoid. If OK, clear memory

and recheck for code(s). If no Code 23, circuit is OK.

Code 23, M/C Solenoid Circuit Low - Flow Chart. Scheme 100

CODE 24 - VEHICLE SPEED SENSOR (VSS)

Note. Disregard a Code 24 set when drive wheels are not turning.

The ECM applies and monitors 12 volts on circuit 437. Circuit 437 connects to the vehicle speed sensor which alternately grounds circuit 437 when the drive wheels are turning. This pulsing action takes place about 2000 times per mile and the ECM calculates vehicle speed based on the time between pulses.

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

1. This test monitors the ECM voltage on circuit 437. with the wheels turning, the pulsing action varies the voltage. This variation is greater at low speeds to an average of 4-6 volts at about 20 mph (32 km/h).
2. This test checks for a grounded circuit. A voltage of less than 1 volt indicates that circuit 437 is shorted to ground. Disconnect circuit 437 at the VSS, the VSS is faulty if the voltage now reads above 10 volts. If the voltage remains less than 10 volts, then circuit 437 wire is grounded. If the wire is not grounded, check for a faulty ECM connector or ECM.
3. A steady 8-12 volts at the ECM connector indicates circuit 437 is open or a faulty VSS.
4. Normal voltage is 1-6 volts and varying. This may indicate an intermittent problem if code 24 is shown.

Code 24, Vehicle Speed Sensor (VSS) - Flow Chart. Scheme 101

Note. To Prevent Misdiagnosis, The Technician Should Identify The Type Of Vehicle Speed Sensor Used Prior To Using This Chart. Disregard Code 24 Set When Drive Wheels Are Not Turning.

Code 24, Vehicle Speed Sensor (VSS) - Flow Chart. Scheme 102

VEHICLE SPEED SENSOR (VSS) (MODELS W/ DIGITAL CLUSTER)

Vehicle speed is sensed by a Vehicle Speed Sensor (VSS). This is comprised of a sensor unit mounted on the transmission, and a VSS Buffer mounted behind the instrument panel (I.P.). The Buffer is supplied 12 volts by the ignition and the ECM. The output from the Buffer to the ECM is a "toggling" of voltage. As the vehicle speed increases the 12 volt signal from the ECM is turned "ON" and "OFF", the faster the speed, the more rapidly the signal toggles. This tells the ECM how fast the vehicle is going. Code 24 says that the ECM has seen the following

1. Vehicle Speed Signal (voltage at term. "16") not rising and falling.
2. RPM within an upper and lower limit.
3. Engine load (TPS) above a given value.
4. Not in Park or Neutral.
5. For more than a given time.

This could keep the Torque Clutch Converter from applying and affect idle speed control motor.

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

1. This test checks if there is a VSS signal to the ECM while the drive wheels are turning. Normal voltage will vary from under 3 volts to more than 6 volts as the wheels turn. If the voltage varies while the wheels are turned, the problem is not in the VSS circuit. Fault could be ECM connector, the ECM or TPS setting.
2. This test checks for proper voltage from ECM to Buffer connector term. "F". If the voltage output from the ECM to the Buffer is in the normal 10-12 volt range the fault is in the buffer connections or the buffer. Low voltage indicates a ground or open to or in the ECM.

Code 24, Vehicle Speed Sensor (VSS) (Digital Cluster). Scheme 103

Code 24, Vehicle Speed Sensor (VSS) (Digital Cluster). Scheme 104

VEHICLE SPEED SENSOR (VSS) (MODELS W/ INTEGRAL BUFFER)

Vehicle speed is sensed by a Vehicle Speed Sensor (VSS) located behind the instrument panel (I.P.) cluster. The VSS is supplied with 12 volts from the ignition and the ECM. The output from the VSS to the ECM is a "toggling" of the voltage. As the speedometer turns, the 12 volt signal from the ECM is turned "ON" and "OFF". The faster the vehicle speed, the more rapidly the signal toggles. Code 24 says that the ECM has seen the following

1. Vehicle Speed Signal (voltage at term. "16") not rising and falling.
2. RPM within an upper and lower limit.
3. Engine Load (TPS) above a given value.
4. Not in Park or Neutral.
5. For more than a given time.

This condition can keep the Transmission Clutch Converter (TCC) from applying and affect idle speed control motor operation on deceleration.

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

1. This test checks for a VSS signal to ECM while turning drive wheel. Normal voltage will vary from under 3 volts to over 6 volts as wheel is turned. The faster the wheel is spun, the less the variation will be. If the voltage varies while the wheel is turned, the problem is not in the VSS circuit. Fault could be an ECM connection, the ECM or TPS setting.
2. Checking voltage at the VSS connector, determines which part of the circuit is at fault. Term. "A" is a buffered 12 volt source from the ECM and term. "C" is a 12 volt ignition source. Terminal "B" is ground.

Code 24, Vehicle Speed Sensor (VSS) (Integral Buffer). Scheme 105

Code 24, Vehicle Speed Sensor (VSS) (Integral Buffer). Scheme 106

FLOW CHART 24B - PARK/NEUTRAL CIRCUIT (P/N)

The P/N switch is closed when the gear selector is in Park or Neutral. One side of the switch is connected to the ECM which supplies a buffered 12 volts, the other side is grounded. The P/N switch is an input to the ECM. When the voltage at ECM term. "H" is high (12 volts), the ECM allows activation, at the proper time, of other controls such as TCC, EST, VSS and others.

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

1. This test checks for good P/N circuit. When the switch is closed in Park and Neutral, the voltage across the P/N switch terminals should be low, usually less than 1 volt. When the switch is open in Drive and Reverse, voltage should be about battery voltage.
2. This step separates a faulty switch, or switch adjustment, from a faulty electrical circuit or ECM. Normal voltage across the terminals of the connector, when removed from the P/N switch, should be about battery voltage.

Flow Chart 24B, Park/Neutral (P/N) Circuit. Scheme 107

Flow Chart 24B, Park/Neutral (P/N) Circuit. Scheme 108

CODE 32 - BARO SENSOR

Note. The BARO sensor reacts like a MAP sensor in that it measures highest voltage when barometric pressure is highest.

Code 32 says that the ECM has seen a BARO pressure (measured in volts) too low at term. "1" of the ECM.

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

1. This test checks voltage output at the sensor. Voltage normally falls within the middle range on table.
2. This test checks for change in voltage at sensor with reduced barometric pressure (applied vacuum). Normal change should be 1.2-2.3 volts. If change is within specifications, fault is not in sensor, but in wiring or ECM.
3. This test determines if fault is in wiring to sensor, ECM connections or ECM.
4. Measures output of sensor with circuit open to ECM. This is to determine if the fault is in the circuit to ECM term. "1" or the ECM, as would be the case if the voltage increased in this step.
5. Takes the sensor out of the circuit to check for proper 5 volt supply voltage from the ECM. With 5 volt reference voltage, sensor is faulty; if not, the circuit from the ECM, or ECM itself, is at fault.

Code 32, BARO Sensor. Scheme 109

Code 32, BARO Sensor (1 Of 2). Scheme 110

Code 32, BARO Sensor (2 Of 2). Scheme 111

CODE 34 - DIFFERENTIAL PRESSURE (VACUUM) SENSOR

Code 34 says that the ECM has seen the following

1. Pressure outside a specified voltage range (seen by ECM as voltage at term. "20").
2. Engine RPM less than a given value.
3. Engine at operating temperature.
4. All the above for a time greater than specified.

The VAC sensor measures the difference in pressure between atmosphere and manifold. The vacuum sensor supplies high voltage at high vacuum. High voltage increases spark advance.

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

1. This test checks output of sensor at idle to determine if sensor is within specification. Normal sensor will read less than 1 volt with key "ON", engine "OFF" and over 3 volts with engine idling (15 in. Hg minimum).
2. Normal sensor will drop below 1 volt with no vacuum.
3. This test checks for a ground in wire from term. "B" of vacuum sensor to ECM. Line is open if voltage is over 2 volts.
4. This test checks to see if the fault is in the sensor, the ECM wiring, or the ECM. If the voltage goes over 2 volts with the sensor disconnected, the sensor or sensor connections are faulty.

Code 34, Differential Pressure (VAC) Sensor. Scheme 112

Code 34, Differential Pressure (VAC) Sensor. Scheme 113

CODE 34 - MAP SENSOR CIRCUIT (3.0L & 3.8L ONLY)

Code 34 says that the ECM has seen the following

1. Pressure outside a specified voltage range (seen by ECM as voltage at term. "20").
2. Engine RPM less than a given value.
3. Engine at operating temperature.
4. All the above for a time greater than specified.

Too high a voltage could cause poor performance because of decreased spark advance and wrong fuel control. Too low a voltage could cause detonation because of too much spark advance and poor performance because of poor fuel control.

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

1. This step measures the voltage of the MAP sensor as a means of comparison to its known voltage range. A good sensor will fall about mid-way in voltage range given in the chart. Measurement must be made with the sensor harness connected and jumpers installed.
2. Applying 10 in. Hg to the sensor should reduce the voltage output of the sensor 1.2-2.3 volts from what was recorded in Step 1). The sensor has its highest output when manifold pressure (lack of vacuum) is at its highest. Voltage should change as soon as the vacuum is changed. A sluggish sensor could cause detonation and/or poor performance. Rapid voltage changes can only be measured with a DVM.
3. This step checks the voltage at the ECM. Under 2 volts indicates an open in the wire to term. "20". A reading over 2 volts indicates the wiring is okay and fault is in the ECM connections or the ECM.
4. This step checks to determine if the source of low output from the MAP sensor is a ground in the circuit to ECM term. "20" or the ECM. This would be indicated by opening the circuit to term. "20" and noting a voltage increase to normal range when measured at the sensor.
5. This step determines if the circuit from the 5 volt reference in the ECM and back through term. "22" is complete. Normal reading would be about 5 volts.

Code 34, MAP Sensor Circuit (3.0L & 3.8L Only). Scheme 114

Code 34, MAP Sensor Circuit (3.0L & 3.8L Only) (1 Of 2). Scheme 115

Code 34, MAP Sensor Circuit (3.0L & 3.8L Only) (2 Of 2). Scheme 116

CODE 35 - IDLE SPEED CONTROL CIRCUIT (3.0L & 3.8L ONLY)

Code 35 indicates that the ECM has seen the voltage at ECM terminal "8" continually low with the throttle open. This indicates that the circuit through the ISC throttle switch is grounded. The voltage should go to 12 volts when the switch opens. A grounded circuit will cause stalling because the ECM will retract the ISC plunger completely resulting in low idle speed.

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

1. This step separates a shorted ISC throttle switch from a TPS/MAP/VAC problem. If the "SERVICE ENGINE SOON" light appears at idle on a restart, the fault is in the TPS/MAP/VAC circuits. Due to ECM calibration, a Code 35 could appear before a 21, 32 or 34 with a faulty TPS or faulty MAP/VAC sensor ground circuit.
2. This step checks for an open ground in circuit to ECM or ECM itself. If the test light is "ON", the fault is in the TPS circuit even though the conditions above may have set a Code 35.
3. This test verifies an ISC throttle switch failure. Raising RPM above 1200 takes the throttle off contact with the ISC. It also keeps a Code 21 from being set when TPS is depressed.
4. This step checks for a malfunctioning ISC nose switch with the connector off of the ISC motor. An ohmmeter should read infinite resistance (open circuit) when the throttle is moved off of the nose switch (and virtually zero with it closed).
5. With the harness disconnected, the voltage from term. "B" to "A" should be about 12 volts.

Code 35, Idle Speed Control Circuit (3.0L & 3.8L Only. Scheme 117

Code 35, Idle Speed Control Circuit (3.0L & 3.8L Only. Scheme 118

CODE 41 - NO DISTRIBUTOR REFERENCE SIGNAL

Code 41 says that there are no distributor references pulses to the ECM at a specified engine vacuum. This code could set with the key "ON", engine "Not Running" if the MAP or vacuum sensor was indicating "Engine Running" voltage with the key just "ON". With a constant open or ground in the reference signal circuit, Code 12 would be set along with 41. Use Chart 12 if 12 and 41 are set. Code 41 alone indicates the problem is intermittent. When the distributor reference line signal is lost, the engine runs full rich and with retarded (base) spark timing. The result is poor performance, poor fuel economy, and possibly rotten egg odor from the exhaust.

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

1. This test checks to see if MAP or vacuum sensor voltage changes with loss of vacuum supply. A good sensor will change voltage at terms. "A" to "B" by 1 volt or more.
2. This test checks for cause of an intermittent open or ground in the distributor circuit. This includes the Hall Switch if so equipped. Fault could also be a MAP or vacuum sensor that is intermittently stuck, at the same voltage output as an engine "running", when the key is only "ON". This condition will produce no reference signal. Terminals must be removed from connector to properly check them. The distributor pick-up coil should also be checked.

Code 41, No Distributor Reference Signal. Scheme 119

Code 41, No Distributor Reference Signal. Scheme 120

CODE 42 - ELECTRONIC SPARK TIMING (EST)

Code 42 says that the ECM has seen

1. Open or grounded By-pass Circuit (term. "11").
2. Open or grounded EST Circuit (term. "12").

With a grounded EST Circuit, the engine may not run. A grounded EST may sometimes not set a code unless cranked 10 seconds or longer with circuit grounded.

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

1. This checks operation of EST. Grounding the "test" terminal causes timing to go to a fixed value which is normally different from that obtained with EST operating. Therefore, the timing should change. Usually the change can be heard in engine RPM. If so, the timing change does not have to be checked.
2. This step eliminates the ECM and ECM connections from the module input. By jumpering terms. "A" and "B", the distributor reference signal is fed directly into the EST line of the module. By putting voltage through the test light on term. "C" of the harness, the module is switched to the EST mode and the vehicle should run. If the engine stops, there is no EST signal reaching the module due to open or poor connections, or the module is faulty.
3. By removing the jumper, you are opening the EST signal, and the engine should stop.
4. The engine ran when the module was jumpered. The problem is not in the distributor (if the correct HEI module is installed). The wrong HEI module can set a Code 42.

Code 42, Electronic Spark Timing (EST). Scheme 121

Code 42, Electronic Spark Timing (EST). Scheme 122

CODE 43 - ELECTRONIC SPARK CONTROL (ESC)

Code 43 indicates that the Electronic Spark Control (ESC) retard signal has been seen by the ECM for too long a period of time. When voltage at term. "L" at the ECM is low, spark is retarded. Normal voltage in non-retard mode is about 7.5 volts or more.

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

1. Normal voltage would be over 7.5 volts. If 7.5 volts is present at term. "L", the reason for a Code 43 is a poor connection to ECM or faulty ECM.
2. Over 6 volts indicates an overly sensitive knock sensor or controller, or noise in the engine that triggers knock sensor.
3. This test checks for grounded ECM.
4. This test checks for an open in wire from ESC to ECM. If over 6 volts was obtained at term. "C" of the ESC, the fault is an open to term. "L" of ECM.
5. This test checks for 12 volt ignition source to ESC term. "B". Reading at term. "B" should be battery voltage.
6. This checks to see if spark retard is due to engine knock or a faulty knock sensor. If by disconnecting the knock sensor spark advances, fault is in engine "noise" or sensor. Normally no increase would be noted.
7. This checks to see if spark retard is due to "noise" on ESC to knock sensor line or a faulty ESC controller. By removing terminal "E" from the connector, the determination can be made. If spark advances, check for improper routing of knock sensor signal wire.

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

Code 43, Electronic Spark Control (ESC) Flow Chart. Scheme 124

CODE 44 - LEAN EXHAUST INDICATION

Code 44 indicates that the ECM has seen O2 sensor voltage under the following conditions

1. Voltage lower than specified.
2. Closed Loop.
3. Above a specified TPS value.
4. For a time longer than specified.

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

1. A fixed dwell of under 10° indicates the problem is still present. A fixed dwell under 10° at idle, with dwell varying at 3000 RPM, usually indicates an intake leak. Check this area prior to replacing O2 sensor.
2. This test checks if the ECM is able to respond to a rich condition caused by choking the engine. If it does, the problem is a lean engine condition, NOT ELECTRICAL.
3. If dwell increases to over 50° with heavy choking, the fault is an air leak. If air is going to exhaust ports, disconnect the solenoid(s) for the air control valve. If air still goes to the ports, air valve is faulty.
4. This step puts a rich O2 signal (about 1 volt) into terminal "9" of the ECM. Dwell should increase (lean command).

Code 44, Lean Exhaust Indication Flow Chart. Scheme 125

Code 44, Lean Exhaust Indication Flow Chart. Scheme 126

CODE 45 - RICH EXHAUST INDICATION

Code 45 indicates that the ECM has seen

1. High oxygen sensor voltage.
2. More than specified time (about 2 minutes).
3. Above a specified TPS value.
4. Closed loop.

A high voltage can be caused by a rich exhaust or an O2 sensor contaminated with silicone.

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

1. Dwell under 50° indicates that engine should be checked for cause of intermittent rich condition; purge or bowl vent valves leaking, fuel in crankcase, fuel in evaporative canister, or sticking mixture control solenoid metering rods.
2. This step tests ECM response to a lean engine condition. A drop in dwell indicates that ECM and O2 sensor are not faulty.
3. This step tests ECM response to a lean O2 signal (low voltage). If no dwell change with a grounded lead to O2 sensor terminal "9", fault is in the ECM. Open O2 sensor wire would have set a Code 13.
4. This step checks voltage from the ECM at the O2 sensor harness. Normal voltage at this point is the ECM bias voltage for no O2 signal, approximately .45 volt. If voltage is high, the wire to the ECM could be shorted to battery voltage, or ECM is faulty.

Code 45, Rich Exhaust Indication Flow Chart. Scheme 127

Code 45, Rich Exhaust Indication Flow Chart. Scheme 128

CODE 51 - FAULTY PROM

Code 51 sets if any of the following occur

1. Faulty PROM unit.
2. PROM unit improperly installed (may not set a code if installed backward).
3. Some PROM pins not making contact (i.e. bent).

Note. Always check to see that the PROM pins are not bent and inserted properly into ECM. Make sure the PROM is installed in the proper direction as shown in the chart.

Code 51, PROM Removal & Installation. Scheme 129

CODE 53 - EXHAUST GAS RECIRCULATION (EGR) VACUUM CONTROL

The EGR Vacuum Control is an ECM controlled solenoid that pulses manifold vacuum to the EGR valve. The control is always de-energized (EGR off) in Park or Neutral and at idle. The ECM controls the EGR vacuum by completing the ground to energize the solenoid. When the solenoid is energized, manifold vacuum opens the EGR valve. Part of the control is a vacuum diagnostic switch. Its purpose is to signal the ECM when vacuum is actually being applied to the EGR valve.

Code 53 will be set if the EGR diagnostic vacuum switch senses vacuum at idle, or if it does not sense vacuum in gear with moderate to heavy engine load, but less than WOT.

The EGR valve is energized based on the following inputs: Engine running above idle, but less than WOT, engine coolant temperature 42.5°C (108°F) or above, and transmission in gear.

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

1. Check for presence of vacuum at idle. Normally there is no vacuum to the EGR at idle.
2. By grounding the diagnostic "test" terminal, the ECM will normally energize the solenoid. The test light should be "ON" if the solenoid circuit is okay.
3. Check for a complete circuit to the vacuum switch. If the circuit is complete, the reading will be about battery voltage.
4. This test checks for a faulty vacuum switch by substituting a vacuum gauge. The test light should be "OFF" if the switch is good.

Code 53, EGR Vacuum Control Flow Chart (1 Of 2). Scheme 130

Code 53, EGR Vacuum Control Flow Chart (2 Of 2). Scheme 131

1. Check Vacuum Lines For Proper Routing, Leaks Or Restrictions
2. Check EGR Valve For Being Stuck Or Leaking
3. Check For A Minimum Of 7" Hg Vacuum To EGR Solenoid, At Part Throttle

Code 53, EGR Vacuum Control Flow Chart (1 Of 2). Scheme 132

Code 53, EGR Vacuum Control Flow Chart (2 Of 2). Scheme 133

Code 53, EGR Vacuum Control Circuit Diagram. Scheme 134

CODE 54 - M/C SOLENOID CIRCUIT HIGH

Code 54 will be set if there is constant high voltage at ECM terminal "18". A short circuit to 12 volts will cause M/C solenoid to remain in the full rich position.

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

1. This test checks the M/C solenoid resistance to determine if the fault is in the solenoid or ECM harness/ECM. Normal reading for a solenoid is 18-32 ohms. NOTE: After replacing a faulty M/C solenoid, a system performance test is necessary to be certain the M/C solenoid was the only faulty part. Solenoid may have caused the ECM to fail, this will reset code.
2. This test checks if reason for high voltage to term. "18" is a faulty ECM or a short to 12 volts on that wire. If the test light to ground lights at the M/C solenoid test lead with both ends of harness disconnected, there is a short to 12 volts in the wire.

Code 54, M/C Solenoid Circuit High. Scheme 135

Code 54, M/C Solenoid Circuit High. Scheme 136

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 137

Flow Chart C1D, MAP & BARO Output Check. Scheme 138

Flow Chart C1D, MAP & BARO Output Check. Scheme 139

Flow Chart C1E, Differential Pressure Sensor (VAC) Check. Scheme 140

Flow Chart C1E, Differential Pressure Sensor (VAC) Check. Scheme 141

Flow Chart C2A, Idle Speed Control (ISC) Check (1 Of 2). Scheme 142

Flow Chart C2A, Idle Speed Control (ISC) Check (2 Of 2). Scheme 143

Flow Chart C2A, Idle Speed Control (ISC) (1 OF 2). Scheme 144

Flow Chart C2A, Idle Speed Control (ISC) (2 OF 2). Scheme 145

Chart C2B, Throttle Kicker (5.0L VIN H or G & 5.7L VIN 6). Scheme 146

Chart C2B, Throttle Kicker (5.0L VIN H or G & 5.7L VIN 6) (1 Of 2). Scheme 147

Chart C2B, Throttle Kicker (5.0L VIN H or G & 5.7L VIN 6) (2 Of 2). Scheme 148

Flow Chart C2C, Idle Load Compensator (5.0L VIN Y) (1 Of 2). Scheme 149

Flow Chart C2C, Idle Load Compensator (5.0L VIN Y) (2 Of 2). Scheme 150

Flow Chart C2C, Idle Load Compensator (5.0L VIN Y) (1 Of 2). Scheme 151

Flow Chart C2C, Idle Load Compensator (5.0L VIN Y) (2 Of 2). Scheme 152

Chart C2C, Idle Load Compensator Ckt Diagram (5.0L VIN Y). Scheme 153

Flow Chart C2D, Rear Vacuum Break (5.0L VIN Y & 9). Scheme 154

Flow Chart C2D, Rear Vacuum Break (5.0L VIN Y & 9). Scheme 155

Flow Chart C2E-1, 2.8L Throttle Kicker (ISC) (1 of 2). Scheme 156

1. If Air Conditioning (A/C) Is Not Operating, Repair It Before Checking Throttle Kicker
2. Make Visual Inspection Of Hoses And Electrical Harness For Condition And Connections

Flow Chart C2E-1, 2.8L Throttle Kicker (ISC) (1 Of 2). Scheme 157

Flow Chart C2E-2, 2.8L Throttle Kicker (ISC) (2 of 2). Scheme 158

Flow Chart C2E-2, 2.8L Throttle Kicker (ISC) (2 of 2). Scheme 159

Flow Chart C2F, TPS Enrichment. Scheme 160

Flow Chart C2F, TPS Enrichment. Scheme 161

Flow Chart C3, Canister Purge Valve. Scheme 162

Flow Chart C3, Canister Purge Valve. Scheme 163

Flow Chart C4A, Ignition System (Integral Coil). Scheme 164

Flow Chart C4A, Ignition System (Integral Coil) (1 Of 2). Scheme 165

Flow Chart C4A, Ignition System (Integral Coil) (2 Of 2). Scheme 166

Flow Chart C4A, Ignition System (Integral Coil) Ckt Diagram. Scheme 167

Flow Chart C4B, Ignition System (External Coil). Scheme 168

Flow Chart C4B, Ignition System (External Coil) (1 Of 2). Scheme 169

Flow Chart C4B, Ignition System (External Coil) (2 Of 2). Scheme 170

Flow Chart C4B, Ignition System (External Coil) Ckt Diagram. Scheme 171

Flow Chart C4C, EST Performance. Scheme 172

Flow Chart C4C, EST Performance. Scheme 173

Flow Chart C5, Knock/Poor Performance/Economy - No Code 43 Electronic Spark Control (ESC). Scheme 174

Note. This chart is used for diagnosis of engine knock, poor performance or poor fuel economy (No Code 43). Only after all causes have been checked, i.e., timing, EGR, MAP engine temperature etc.

Flow Chart C5, Knock/Poor Performance/Economy - No Code 43 Electronic Spark Control (ESC). Scheme 175

Flow Chart C6A, Air Management (w/Elect Divert & Switching Valve). Scheme 176

Flow Chart C6A, Air Management (w/Elect Divert & Switching Valve) (1 Of 2). Scheme 177

Flow Chart C6A, Air Management (w/Elect Divert & Switching Valve) (2 Of 2). Scheme 178

Chart C6A, Schematic - Air Management (w/Elect Divert & Switching Valve). Scheme 179

Flow Chart C6B, Air Management (w/Pressure Operated Divert & Switching Valve). Scheme 180

Flow Chart C6B, Air Management (w/Pressure Operated Divert & Switching Valve). Scheme 181

Flow Chart C7A, PWM EGR (Exc. 3.0L VIN E & 3.8L VIN A). Scheme 182

Flow Chart C7A, PWM EGR (Exc. 3.0L VIN E & 3.8L VIN A) (1 Of 2). Scheme 183

Flow Chart C7A, PWM EGR (Exc. 3.0L VIN E & 3.8L VIN A) (2 Of 2). Scheme 184

Flow Chart C7B, EGR Valve (3.0L VIN E & 3.8L VIN A). Scheme 185

Flow Chart C7B, EGR Valve (3.0L VIN E & 3.8L VIN A). Scheme 186

Flow Chart C7C, EGR Valve (5.0L VINs Y & 9). Scheme 187

Flow Chart C7C, EGR Valve (5.0L VINs Y & 9). Scheme 188

Flow Chart C8A1, TCC Electrical Diagnosis (1 of 2). Scheme 189

Flow Chart C8A1, TCC Electrical Diagnosis (2 of 2). Scheme 190

Flow Chart C8A1, TCC Electrical Diagnosis (1 Of 2). Scheme 191

Flow Chart C8A1, TCC Electrical Diagnosis (2 Of 2). Scheme 192

Chart C8A2, TCC Elect Diagnosis Chart & Schematic (3 of 3). Scheme 193

Flow Chart C9A, Electrically Heated EFE. Scheme 194

Flow Chart C9A, Electrically Heated EFE. Scheme 195

Flow Chart C9C, EFE Vacuum Servo With TVS. Scheme 196

Flow Chart C9C, EFE Vacuum Servo With TVS. Scheme 197

Flow Chart C9D, Non-ECM Controlled Electric EFE. Scheme 198

Flow Chart C9D, Non-ECM Controlled Electric EFE. Scheme 199

Flow Chart C10A, A/C Constant Run Relay (3.0L A Series). Scheme 200

Flow Chart C10A, A/C Constant Run Relay (3.0L A Series). Scheme 201

Flow Chart C10B, A/C WOT Relay (3.0L A Series). Scheme 202

Flow Chart C10B, A/C WOT Relay (3.0L A Series). Scheme 203

Flow Chart C10C, A/C Cut-Out Relay (1 Of 2). Scheme 204

Flow Chart C10C, A/C Cut-Out Relay (2 Of 2). Scheme 205

Flow Chart C10C, A/C Cut-Out Relay (1 Of 2). Scheme 206

Flow Chart C10C, A/C Cut-Out Relay (2 Of 2). Scheme 207

Flow Chart C10D, A/C WOT Relay (Except 3.0L A Series). Scheme 208

Flow Chart C10D, A/C WOT Relay (Except 3.0L A Series). Scheme 209

Flow Chart C12A1, Coolant Fan Functional. Scheme 210

Flow Chart C12A1, Coolant Fan Functional. Scheme 211

Flow Chart C12A2, Coolant Fan, No Low Speed (Perform C12A1 First). Scheme 212

Flow Chart C12A2, Coolant Fan, No Low Speed (Perform C12A1 First). Scheme 213

Flow Chart C12A3, Coolant Fan, No High Speed (Perform C12A1 First). Scheme 214

Flow Chart C12A3, Coolant Fan, No High Speed (Perform C12A1 First). Scheme 215

Coolant Fan Component Locations & Schematic For C12B Charts. Scheme 216

Flow Chart C12B-1, Coolant Fan Functional Check (3.0L A Series). Scheme 217

1. Check Coolant Level And Degrees Or Protection
2. Check Radiator, Cap And Fan For Obstruction
3. Check All Electrical Components For Proper Connections
4. Repeat Functional Check After Any Repair

Flow Chart C12B-1, Coolant Fan Functional Check (3.0L A Series). Scheme 218

Flow Chart C12B-2, Coolant Fan Always On (Perform C12B-1 First). Scheme 219

Flow Chart C12B-2, Coolant Fan Always On (Perform C12B-1 First). Scheme 220

Flow Chart C12B-3, Coolant Fan No Low Speed (Perform C12B-1 First). Scheme 221

Flow Chart C12B-3, Coolant Fan No Low Speed (Perform C12B-1 First). Scheme 222

Flow Chart C12B-4, Coolant Fan No High Speed (Perform C12A1 First). Scheme 223

Flow Chart C12B-4, Coolant Fan No High Speed (Perform C12A1 First). Scheme 224

Full Function ECM Terminal Identification 2.8L (VIN X). Scheme 225

Full Function ECM Terminal Identification 3.0L (VIN E). Scheme 226

Full Function Terminal Identification 3.8L (VIN A). Scheme 227

Full Function Terminal Identification 5.0 (VIN G). Scheme 228

Full Function Terminal Identification 5.0 (VIN H) & 5.7L. Scheme 229

Full Function Wiring Diagram - 2.8L Engine. Scheme 230

Full Function Wiring Diagram - 3.0L & 3.8L Engines. Scheme 231

Note. In Fig. (Scheme 232), the ground symbol on the Pin 22 wire going to the VAC Sensor should be removed. The EGR Cutout relay should be removed from the diagram. It does not exist. (Scheme 233)for revision.

Full Function Wiring Diagram - 5.0L & 5.7L Engines. Scheme 232

VAC Sensor Wiring Diagram - 5.0L & 5.7L Engines. Scheme 233