2.5l Tbi Tests W/codes Pontiac 6000 I

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 Operating Conditions Sensed & Systems Controlled. Scheme 216

Schematic of Computer Command Control System. Scheme 217

Sectional View of Mixture Control Solenoid. Note air bleed above main metering rod. Scheme 218

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 219

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 219) 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 219): 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 "longterm" 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 ONCar Diagnostics have found. These charts include

1. Charts which fix a problem when the ONCar Diagnostics don't work.
2. Charts where a stored trouble code leads you to a particular problem.
3. Charts which are used because the Field Service Mode 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).

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.

"NONSCAN" DIAGNOSTIC CIRCUIT CHECK (A/F/J/N/P BODY)

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 the chart and using it correctly will reduce diagnostic time and prevent unnecessary replacement of parts.

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 the CCC 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: A) 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. B) 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. C) "SERVICE ENGINE SOON" light off indicates that exhaust is lean. Oxygen sensor will be less than .35 volts and steady. See Code 44. D) "SERVICE ENGINE SOON" light on steady indicates that exhaust is rich. Oxygen sensor signal will be above .55 volts and steady. See Code 45.
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

"NONSCAN" Diagnostic Circuit Check Flow Chart (All). Scheme 220

"NONSCAN" Diagnostic Circuit Check Flow Chart (All). Scheme 221

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 DATA tables. They also furnish information on output device (solenoids and motors) status. Status parameters, however, are only an indication that output signals have been sent to devices by the ECM. It does not indicate if devices have responded properly to that signal. This will need to be verified at output device using a voltmeter or test light.

Note. Code 12 should always exist when ALDL is grounded with key on and engine not running but may not be indicated by all makes of scan tester.

If trouble codes are not present, this is not an indication that there is not a problem. CCC related problems are about 20 percent codes and 80 percent driveability. Sensors that are out of specification WILL NOT set a trouble code but WILL cause driveability problems. Use of a scan tester is easiest method of checking sensor specifications and other data parameters. Tester is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See the SCAN TESTER - TEST DATA PARAMETERS table below.

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

SCAN TESTER - TEST DATA PARAMETERS

Note. Information in the following tables 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

"SCAN" DIAGNOSTIC CIRCUIT CHECK (A/F/J/N/P BODY)

The "SCAN" diagnostic circuit check is an organized approach for identifying fuel injection problems using an assembly line communication link (ALCL). This communication link can provide diagnostic information for display on any scan device or tool designed for this purpose. The tool plugs into ALCL connector located below instrument panel. If a stored code is displayed, code definitions will aid in determining if fault is still present (hard failure) or result of an intermittent condition not normally diagnosed using code charts.

1. If scan tool is not operating, check on another vehicle. If okay, the cigar lighter socket should be checked for 12 volts and a good ground. If scan tool reads "no data" or "no ALCL" with ignition on, check serial data wire for an open or short to ground between ALCL terminal "E" and ECM.

Also check for an open diagnostic test terminal for ALCL terminal "B" and ECM. With ignition on, serial data line (ALCL terminal "E") should have a varying 2-5 volts, and diagnostic line (ALCL terminal "B") about 5 volts.

"SCAN" Diagnostic Circuit Check Flow Chart (All). Scheme 222

"SCAN" Diagnostic Circuit Check Flow Chart (All). Scheme 223

CHART A1 - NO "SES" LIGHT (A/F/J/N/P BODY)

The "SERVICE ENGINE SOON" light should come on when ignition is turned on and engine is not running. Battery voltage is supplied directly to the bulb. The ECM controls the light by grounding circuit No. 419.

If engine runs, a no "SERVICE ENGINE SOON" light condition indicates a defective bulb, blown fuse or open control circuit No. 419. If engine cranks but will not run, no "SERVICE ENGINE SOON" light indicates a blown battery fuse, blown fusible link, ECM ignition fuse blown, battery circuit No. 340 to ECM open, ignition circuit No. 439 to ECM open or poor connection to ECM.

1) Solenoids and relays are turned on or off by ECM, using electronic switches called "drivers". Each driver is part of a group of 4, called "QuaDDrivers". Failure of one (1) driver can damage other drivers in set. Solenoid and relay coil resistance must be more than 20 ohms, as less resistance will cause early failure of ECM drivers.

Flow Chart A1: No "SES" Light (All Models). Scheme 224

Flow Chart A1: No "SES" Light (All Models). Scheme 225

CHART A2 - NO CODE 12, "SES" ALWAYS ON (A/F/J/N/P BODIES)

The "SERVICE ENGINE SOON" light should come on when ignition switch is in the "ON" position and engine is not running. Battery voltage is directly supplied to bulb. The ECM controls the light by grounding circuit No. 419. With diagnostic terminal grounded, light should flash Code 12, followed by other trouble codes stored in memory. A steady light indicates a grounded circuit No. 419 or an open diagnostic circuit No. 451.

1. If the light goes off when the ECM connector is disconnected, then circuit No. 419 is not shorted to ground. Check connector terminals physically for proper contact.
2. This step checks for an open diagnostic circuit No. 451.
3. At this point wiring is okay. Problem may be a faulty ECM or PROM. If Code 51 is stored when PROM is removed, replace PROM.
4. Solenoids and relays are turned on or off by ECM, using electronic switches called "drivers". Each driver is part of a group of 4, called "QuaDDrivers". Failure of one (1) driver can damage other drivers in set. Solenoid and relay coil resistance must be more than 20 ohms, as less resistance will cause early failure of ECM drivers.

Flow Chart A2: No Code 12, "SES" Light on Steady (All). Scheme 226

Flow Chart A2: No Code 12, "SES" Light On Steady (All). Scheme 227

CHART A3 - CRANKS BUT WON'T RUN (A/F/J/N/P BODY)

1. 1) A "SERVICE ENGINE SOON" light on checks for ignition and battery supply to ECM.
2. 2) Fuel spray from injector indicates that fuel is available, check engine for flooding.
3. 3) While cranking engine there should be no fuel spray with injector disconnected. Replace injector if it sprays or if it drips.
4. 4) If injector is okay, fuel system appears to be operating normally. Using ST125 spark gap tool, check voltage at spark plugs. No spark indicates an HEI problem. If spark is satisfactory, check the following; Throttle Position Sensor (TPS) for sticking or binding in wide open throttle position, coolant sensor "OPEN" signal to ECM using Code 15 chart, check for ice (cold weather) or foreign material in fuel. Engine may start after 5-6 minutes in heated shop. Check for EGR sticking open, open crank signal (cold weather), low fuel pressure or volume (lean air/fuel ratio). See A5.
5. 5) The EFI system is considered okay if no trouble was found. Reconnect injector and look for possible mechanical problems.
6. 6) No spray from injector indicates a faulty fuel system or no ECM control of injector. If test light "blinks" while cranking, ECM control is considered okay. Light may dim while "blinking". Use bulb 1847 or equivalent.

Flow Chart A3: Cranks But Won't Run (All). Scheme 228

Flow Chart A3: Cranks But Won't Run (All). Scheme 229

Chart A3 Schematic: Cranks But Won't Run (All). Scheme 230

CHART A4 - CRANKS BUT WON'T RUN (A/F/J/N/P BODY)

1. 7) Circuit No. 439 supplies ignition voltage to injector. Using a test lamp, probe each connector terminal. Test lamp should light on one (1) terminal, confirming voltage at connector. The ECM injector circuit No. 467 may be open. Reconnect injector. Using test lamp, probe terminal 8 of White ECM connector. A light at this point indicates that injector drive circuit is okay.
2. 8) No "blinking" light indicates no ECM control of injector. With voltmeter on AC 2 volt range, voltage should be greater than .7 volts. If voltage is less than .7 volts, there is an open or short to ground in HEI reference circuit No. 430. If circuit is okay, there is an HEI problem.
3. 8A) Disconnect distributor connector. Momentarily touch ECM side of connector, circuit No. 430, with a test lamp connected to 12 volts. Note injector as contact is made. Injector should turn on. If injector turns on, ECM circuit is okay. Connect spark tool ST125 and check for spark. If spark is okay, HEI module is faulty. No spark indicates an HEI problem.

Flow Chart A4: Cranks But Won't Run (All). Scheme 231

Flow Chart A4: Cranks But Won't Run (All). Scheme 232

CHART A5 - FUEL SYSTEM DIAGNOSIS (A/F/J/N/P BODY)

The ECM turns in tank fuel pump on as long as ignition is on and the engine is cranking or running. The ECM will allow the pump to run as long as it receives reference pulses from distributor. If there are no reference pulses, the ECM will shut off the fuel pump within 2 seconds after key is in "ON" position. The fuel pump test terminal is located on left side of engine compartment. When engine is stopped, pump can be turned on by applying battery voltage to test terminal. Improper fuel system pressure will result in one (1) or all of the following symptoms: cranks but will not run, Code 44, Code 45, engine cuts out (may feel like ignition problem), poor fuel economy, loss of power and hesitation.

1. If the fuse is blown, this test will confirm a short to ground on circuit No. 120. To prevent misdiagnosis, be sure fuel pump is disconnected before test.
2. This test determines if pump circuit is ECM controlled. The ECM will turn pump relay on, then turn it off after 2 seconds, if engine is not cranking or running.
3. This step turns fuel pump on, if circuit No. 120 wiring is okay.
4. This step checks for battery voltage at fuel pump relay.

Flow Chart A5: Fuel System Diagnosis. Scheme 233

Flow Chart A5: Fuel System Diagnosis (1 Of 2). Scheme 234

Flow Chart A5: Fuel System Diagnosis (2 Of 2). Scheme 235

Chart A5 Schematic: Fuel System Diagnosis. Scheme 236

CHART A6 - FUEL SYSTEM DIAGNOSIS (A/F/J/N/P BODY)

Note. Continued from CHART A5.

1. 5) This step checks relay ground circuit No. 450.
2. 6) This step checks ECM control of relay through circuit No. 465.
3. 7) The fuel pump circuit includes an engine oil pressure switch. If fuel pump relay fails, the fuel pump will continue to run via oil pressure switch circuit. Relay failure will result in extended cranking times and possible no start condition.
4. 8) This test checks the oil pressure switch to be sure it provides battery feed to fuel pump if pump relay fails.
5. 9) This test checks for open oil pressure switch with ignition off. Should switch stick closed, fuel pump will continue to run and discharge battery.

Flow Chart A6: Fuel System Diagnosis. Scheme 237

Flow Chart A6: Fuel System Diagnosis. Scheme 238

CHART A7 - FUEL SYSTEM DIAGNOSIS (A/F/J/N/P BODY)

Note. Continued from CHART A5.

1. Pressure below 9 psi falls into 2 categories: If regulated pressure is less than 9 psi and volume to injector is adequate, system will run lean and cause Code 44. Engine will be hard to start when cold and have poor overall performance. A restricted fuel flow is causing pressure drop. Normally, a vehicle with fuel pressure of less than 9 psi at idle will not be driveable. However, if pressure drop occurs only when driving, the engine will surge then stop as pressure begins to drop.
2. Restricting the fuel return line allows the fuel pump to develop its maximum pressure. When battery voltage is applied to pump test terminal, pressure should be between 13 to 18 psi.
3. This test determines if high fuel pressure is due to a restricted fuel return line or a throttle body pressure regulator problem.

Flow Chart A7: Fuel System Diagnosis. Scheme 239

FLOW CHART A7: FUEL SYSTEM DIAGNOSIS. Scheme 240

CODE 13 - OPEN O2 CIRCUIT (A/F/J/N/P BODY)

Code 13 will set: at least 2 minutes after engine start, with O2 signal voltage steady between .35 and .55 volt for more than one (1) minute, and with throttle position sensor signal above 6% (1200 RPM). The ECM supplies voltage of about .45 volt between terminals 8 and 15. (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.) The O2 sensor varies the voltage within a range of about one (1) volt (rich exhaust) to .1 volt (lean exhaust). The O2 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.

1. Grounding diagnostic terminal with engine running activates "Field Service Mode". This allows the ECM to confirm either open or closed loop operation using the "SERVICE ENGINE SOON" light.
2. This step verifies that no additional codes are stored, and that Code 13 is intermittent. See the CCC TESTS W/O CODES article in this section.
3. This step simulates a lean exhaust. If ECM and wiring are okay, the ECM will see the lean condition and turn the "SERVICE ENGINE SOON" light off for at least 30 seconds after engine start, and then flash "open loop". It is considered normal if light remains off for a longer period of time before flashing open loop.

Code 13 Flow Chart: Open O2 Circuit. Scheme 241

Code 13 Flow Chart: Open O2 Circuit. Scheme 242

CODE 14 - COOLANT SENSOR SIGNAL VOLT LO (A/F/J/N/P BODY)

The Coolant Temperature Sensor uses a thermistor to control 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 a high signal voltage. As the engine warms, the sensor resistance becomes less. The voltage signal will be about 1-1.5 volts at terminal 4 of ECM. Code 14 will set if signal voltage indicates a coolant temperature above 275°F (135°C) for more than 4 seconds. Coolant temperature is one (1) of the inputs used to control fuel delivery, engine timing (EST), idle (IAC), and converter clutch (TCC).

1. If voltage is above 4 volts, the ECM and wiring are okay. If checking resistance at coolant sensor is difficult because of sensor location, disconnect Black ECM connector and check resistance between terminals 4 and 11.

Code 14 Flow Chart: Coolant Sensor Voltage Low. Scheme 243

Code 14 Flow Chart: Coolant Sensor Voltage Low. Scheme 244

CODE 15 - COOLANT SENSOR SIGNAL VOLT HI (A/F/J/N/P BODY)

The Coolant Temperature Sensor uses a thermistor to control 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 a high signal voltage. As the engine warms, the sensor resistance becomes less and voltage drops. At normal engine operating temperature, voltage will be about 1-1.5 volts at terminal 4 of ECM.

Code 15 will set if signal voltage indicates a coolant temperature less than -24°F (-35°C) for more than 4 seconds or if time since engine start is more than one (1) minute. Coolant temperature is one (1) of the inputs used to control fuel delivery, engine timing (EST), idle (IAC), and converter clutch (TCC).

If coolant circuit No. 410 opens with ignition off, the ECM will see -40°F (-40°C) and deliver fuel for this temperature. If actual temperature is above 20°F (-7°C), the engine will not start due to rich mixture unless "Clear Flood" is used by fully depressing accelerator. Engine will start using "Clear Flood". However, "SERVICE ENGINE SOON" light will not come on and code will not be stored, until engine has run for one (1) minute.

1. If voltage is above 4 volts, the ECM and wiring are okay. If location of sensor makes it hard to check, disconnect Black ECM connector and check resistance between connector terminals 4 and 11.

Code 15 Flow Chart: Coolant Sensor Signal Voltage High. Scheme 245

Code 15 Flow Chart: Coolant Sensor Signal Voltage High. Scheme 246

CODE 21 - TPS SIGNAL VOLT HI (A/F/J/N/P BODY)

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to 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 2 seconds, engine speed is less than 1600 RPM or if MAP is less than 9 psi or equal to a no load condition.

1. This test confirms Code 21, and that fault is present.
2. This test simulates Code 22. If the ECM recognizes the low voltage signal and sets Code 22, the ECM and wiring are okay.

Code 21 Flow Chart: TPS Signal Voltage High. Scheme 247

Code 21 Flow Chart: TPS Signal Voltage High. Scheme 248

Code 21 Schematic: TPS Signal Voltage High. Scheme 249

CODE 22 - TPS SIGNAL VOLT LO (A/F/J/N/P BODY)

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to throttle valve. 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 2 seconds and engine speed is less than 1600 RPM.

1. This test confirms Code 22, and that a fault is present.
2. This test simulates Code 21. If the ECM recognizes high voltage signal and sets Code 21, the ECM and wiring are okay.
3. This test checks for reference voltage from the ECM. To prevent damage to ECM, be sure to disconnect connector when checking circuit wiring for open or shorts to ground.

Code 22 Flow Chart: TPS Signal Voltage Low. Scheme 250

Code 22 Flow Chart: TPS Signal Voltage Low. Scheme 251

CODE 24 - VEHICLE SPEED SENSOR (VSS) (A/F/J/N/P BODY)

The ECM applies and monitors 12 volts on circuit No. 437. Circuit No. 437 connects to Vehicle Speed Sensor (VSS) which alternately grounds circuit when drive wheels are turning. This pulsing action takes place 2000 times per mile. The ECM calculates vehicle speed based on the time between "pulses".

1. This test monitors the ECM voltage on circuit No. 437. With wheels turning, the pulsating action will result in a varying voltage. The variation will be greater at low speeds to an average of 4-6 volts at about 20 MPH.
2. A voltage of less than one (1) volt at ECM connector indicates that circuit No. 437 is shorted to ground. Disconnect 437 at VSS. If voltage now reads above 10 volts, the VSS is faulty. If voltage remains less than 10 volts, circuit No. 437 is grounded. If circuit No. 437 is not grounded, check for faulty ECM connector or ECM.
3. A steady 8-12 volts at ECM connector indicates circuit No. 437 is open or a faulty VSS.
4. This normal voltage condition indicates a possible intermittent problem. Refer to the CCC TESTS W/O CODES article in this section.
5. If "Scan" displays vehicle speed, check park/neutral switch CHART C1A on vehicle with automatic transmission. If switch is okay, check for intermittents.

Code 24 Flow Chart: Vehicle Speed Sensor (VSS). Scheme 252

Code 24 Flow Chart: Vehicle Speed Sensor (VSS). Scheme 253

CODE 33 - MAP SENSOR SIGNAL VOLT HI (A/F/J/N/P BODY)

The Manifold Absolute Pressure (MAP) sensor 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 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 a time greater than 8 seconds and if the TPS voltage indicates throttle is closed. Engine misfire or a low and unstable idle may set Code 33. Disconnect MAP sensor and system will go to backup mode. If misfire or idle condition remains, refer to the CCC TESTS W/O CODES article in this section.

1. This test confirms Code 33, and that fault is present.
2. If the ECM recognizes and sets Code 34, low MAP signal, the ECM and wiring are okay.

Code 33 Flow Chart: MAP Sensor Signal Voltage High. Scheme 254

Code 33 Flow Chart: MAP Sensor Signal Voltage High. Scheme 255

Code 33 Schematic: MAP Sensor Signal Voltage High. Scheme 256

CODE 34 - MAP SENSOR SIGNAL VOLT LO (A/F/J/N/P BODY)

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 set when signal reading is too low and ignition is turned on.

1. This test confirms Code 34, and that fault is present.
2. If the ECM recognizes and sets Code 33, high MAP signal, the ECM and wiring are okay.

Code 34 Flow Chart: MAP Sensor Signal Voltage Low. Scheme 257

Code 34 Flow Chart: MAP Sensor Signal Voltage Low. Scheme 258

CODE 35 - IDLE AIR CONTROL (IAC) (A/F/J/N/P BODY)

Code 35 will set when closed throttle engine speed is 50 RPM above or below correct idle speed for 30 seconds. Following are nominal warm engine idle speeds

A, J & N BODIES NOMINAL IDLE SPEEDS (RPM)

1. Continue with test even if engine will not idle. If idle is too low, "Scan" will display 80 or more counts or steps. If idle is high and a visual check of idle air passage shows a seated valve, locate and correct vacuum leak. If idle is very high, usually above 1400 RPM and IAC valve is not visible in air passage, follow left side of chart. Occasionally an erratic or unstable idle may occur. Engine speed may vary 200 RPM or more up and down. Disconnect IAC. If condition is unchanged, IAC is not at fault. There is a system problem. Proceed to step 3).
2. When engine was stopped, IAC valve retracted (more air) to fixed park position to provide increased airflow during next engine start. A "Scan" will display 95 or more counts and valve should not be visible in idle air passage. Disconnecting IAC will hold valve in retracted or open position, and cause a closed throttle idle speed above 1500 RPM. A "Scan" will now display "0" counts because ECM has tried to reduce idle speed by extending valve. The IAC is okay. The Code 35 is likely a thermac or cruise control vacuum hose disconnect.
3. A slow unstable idle may be caused by a system problem that cannot be overcome by IAC. If IAC is visible in air passage, the chart should locate problem. If valve is not visible, IAC is probably okay. In both cases "Scan" counts will be above 60 counts.

Code 35 Flow Chart: Idle Air Control (IAC). Scheme 259

Code 35 Flow Chart: Idle Air Control (IAC). Scheme 260

CODE 42 - ELECTRONIC SPARK TIMING (EST) (A/F/J/N/P BODY)

Code 42 indicates the ECM has seen an open or short to ground in EST or bypass circuits.

1. This test confirms Code 42, and that fault is present.
2. This test checks for a normal EST ground path through the ignition module. If circuit No. 423 is shorted to ground, reading will be less than 500 ohms.
3. As test lamp voltage touches circuit No. 424, the module should switch. This will cause the ohmmeter to "overrange" if meter is in the 1000-2000 ohm position. A higher ohm range will indicate over 5000 ohms. This test assures that the module "switched".
4. If module did not switch, this step will test for a short in circuit No. 423, an open in circuit No. 424, and a faulty ignition module connection or module.
5. This step confirms that Code 42 is a faulty ECM and not an intermittent problem in circuit Nos. 423 and 424.

Electronic Spark Timing (EST). Scheme 261

Electronic Spark Timing (EST). Scheme 262

CODE 44 - LEAN EXHAUST INDICATION (A/F/J/N/P BODY)

The ECM supplies a voltage of about .45 volt between circuit Nos. 412 and 413. The O2 sensor varies the voltage from one (1) volt (rich exhaust) to .10 volt (lean exhaust). The sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is below 600°F (310°C). An open sensor circuit or cold sensor causes open loop operation. Code 44 is set when O2 sensor signal at ECM is below .2 volts for 50 seconds or more or if time since engine start is one (1) minute or longer.

1. Grounding diagnostic test terminal with engine running activates the "Field Service Mode" and allows the ECM to confirm either open or closed loop operation.
2. A light out or "open loop" indicates presence of fault. Disconnecting O2 sensor will raise signal voltage above .2 volt. If the ECM and wiring are okay, the ECM should recognize the higher voltage, .35 to .55 volt, and flash "open loop" when engine is started.
3. Code 44 may be set by any of the following conditions: circuit No. 413 open (circuit No. 412 voltage will be over one (1) volt), low fuel pressure, fuel contamination, EGR stuck open or malfunctioning MAP sensor. If these items are okay, and instructions at top of chart set Code 44, "SERVICE ENGINE SOON" light is off more than on or flashing "open loop", oxygen sensor is faulty.

Code 44 Flow Chart: Lean Exhaust Indication. Scheme 263

Code 44 Flow Chart: Lean Exhaust Indication. Scheme 264

CODE 45 - RICH EXHAUST INDICATION (A/F/J/N/P BODY)

The ECM supplies a voltage of about .45 volt between circuit Nos. 412 and 413. The O2 sensor varies the voltage from one (1) volt (rich exhaust) to .10 volt (lean exhaust). The sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is below 600°F (310°C). An open sensor circuit or cold sensor causes open loop operation. Code 45 is set when O2 sensor signal at ECM is above .7 volts for one (1) second and time since engine start is one (1) minute or more.

1. Grounding diagnostic test terminal with engine running activates the "Field Service Mode" and allows the ECM to confirm either open or closed loop operation.
2. A steady light or "open loop" indicates presence of fault. Grounding circuit No. 412 causes a low O2 sensor signal voltage. If the ECM and wiring are okay, the ECM should recognize the low voltage, and confirm lean signal by turning "SERVICE ENGINE SOON" light for at least 30 seconds.
3. Code 45 will not be set by a faulty O2 sensor. Code 45 indicates a rich exhaust and diagnosis should begin with these items: fuel pressure, leaking injector, HEI shielding, canister purge saturation, coolant sensor, MAP sensor, and TPS intermittent output.

Code 45 Flow Chart: Rich Exhaust Indication. Scheme 265

Code 45 Flow Chart: Rich Exhaust Indication. Scheme 266

CODE 51 - FAULTY MEMCAL (A/F/J/N/P BODY)

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

CODE 52 - FUEL CALPAK MISSING

Engine idling. Note "Service Engine Soon" light after 10 seconds. If light is off, no trouble found. Check Calpak PROM to insure proper installation.

If light is ON, turn ignition ON and engine OFF. Ground test terminal and note Code. If Code 52 is present, install Calpak PROM in ECM. If other Codes other than Code 52, see appropriate chart.

CODE 55 - ECM (A/F/J/N/P BODY)

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

ECM REPLACEMENT CHECK CHART - C1

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 267

Note. Use this chart only after the normal diagnostic charts have determined that there is an ECM failure.

Ecm Replacement Check Chart C-1. Scheme 268

CHART C1A - PARK/NEUTRAL SWITCH A/T (A/F/J/N/P BODY)

The park/neutral switch contacts are part of neutral start switch, are closed to ground in park or neutral, and open in drive ranges. The ECM supplies ignition voltage through a current limiting resistor to circuit No. 434, and senses a closed switch when voltage on circuit No. 434 drops to less than one (1) volt. The ECM uses this signal as one of the inputs to control IAC and VSS diagnostics.

1. Checks for closed switch to ground in park position. Use an ohmmeter instead of a test light to 12 volts. Resistance will be low indicating continuity to ground.
2. Checks for an open switch in drive range. Use an ohmmeter instead of a test light to 12 volts. Resistance will be high or infinity, indicating an open switch.
3. Checks to this point indicate park/neutral switch and wiring are okay. The ECM signal voltage on circuit No. 434 may be missing. To check, reconnect ECM. Either back probe ECM connector circuit No. 434 with selector in drive or disconnect park/neutral switch. Probe harness connector circuit No. 434 with a voltmeter to ground.

Flow Chart C1A: Park/Neutral Switch (A/T). Scheme 269

Flow Chart C1A: Park/Neutral Switch (A/T). Scheme 270

CHART C1B - 2.5L CRANK SIGNAL (P BODY)

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

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

Flow Chart C1B: 2.5L Crank Signal (P Body). Scheme 271

Flow Chart C1B: 2.5L Crank Signal (P Body). Scheme 272

CHART C1D - MAP OUTPUT CHECK (A/F/J/N/P BODY)

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

1. Check MAP sensor output voltage to ECM. This voltage, without engine running, represents a barometer reading to ECM.
2. Applying 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 273

Flow Chart C1D: MAP Output Check. Scheme 274

CHART C1E - P/S PRESSURE SWITCH (A/F/J/N BODY)

The power steering pressure switch is normally open to ground, and circuit No. 495 will be near battery voltage. Turning steering wheel increases power steering oil pressure, and its load on an idling engine. The pressure switch will close before load can cause an idle problem. Closing switch causes circuit No. 495 to read less than one (1) volt. The ECM will increase idle air rate and retard timing. A pressure switch that will not close, or an open circuit No. 495 or 450 may cause engine to stop when power steering loads are high. A switch that will not open, or a circuit No. 450 or 495 shorted to ground, will cause timing to retard at idle and may effect idle quality.

1. Checks for ECM signal voltage on circuit No. 495, and confirms ground circuit No. 450 is okay.
2. Maximum resistance, or infinity, indicates an open switch.
3. Less than one (1) ohm indicates that switch is closed when power steering pressure is high. Switch is okay.

Flow Chart C1E: P/S Pressure Switch. Scheme 275

Flow Chart C1E: P/S Pressure Switch. Scheme 276

CHART C4B - 2.5L IGNITION SYSTEM CHECK (A/F/N/P BODY)

1. 1) The 2 wires are checked to ensure that an open is not present in a spark plug wire.
2. 1A) If spark occurs with 4 terminal distributor connector disconnected, pickup coil output is too low for EST operation.
3. 2) A spark indicated problem must be distributor cap or rotor.
4. 3) Normally, there should be battery voltage at "C" and "+" terminals. Low voltage would indicate an open or a high resistance circuit from distributor to coil or ignition switch. If "C" terminal voltage was low, but "+" terminal voltage is 10 volts or more, circuit from "C" terminal to ignition coil or ignition coil primary winding is open.
5. 4) Checks for a shorted module or grounded circuit from ignition coil to 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 (1) volt. This could cause ignition coil to fail from excessive heat. With an open ignition coil primary winding, a small amount of voltage will leak through module from "Bat" terminal to tach terminal.
6. 5) Applying a voltage (1.5-8 volts) to module terminal "P" should turn module on, and tach terminal voltage should drop to about 7-9 volts. This test will determine whether module or coil is faulty or if pickup coil is not generating proper signal to turn module on. This test can be performed by using DC battery with to rating of 1.5-8 volts. The use of test light is mainly to allow "P" terminal to be probed more easily Some digital multimeters can also be used to trigger module by selecting ohms, usually the diode position. In this position meter may have voltage across it's terminals, which can be used to trigger module. The voltage in ohm's position can be checked by using a second meter or by checking the manufacture's specification of tool being used.
7. 6) This should turn off module and cause a spark. If no spark occurs, fault is most likely in ignition coil because most module problems would have been found before this point in procedure. A Module Tester (J24642) could determine which is at fault.

Flow Chart C4B: 2.5L Ignition System Check. Scheme 277

Flow Chart C4B: 2.5L Ignition System Check (1 Of 2). Scheme 278

Flow Chart C4B: 2.5L Ignition System Check (2 Of 2). Scheme 279

Chart C4B Schematic: 2.5L Ignition System Check. Scheme 280

CHART C8 - 125C TCC (A/N BODY)

The purpose of automatic transmission/transaxle 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/transaxle and fuel economy of a manual transmission. Fused battery ignition is supplied to TCC solenoid through brake switch, and transmission 3rd gear apply switch. The ECM will engages TCC by grounding circuit No. 422 to energize solenoid.

TCC will engage when vehicle speed is above 45 MPH, engine at normal operating temperature (above 158°F/70°C), throttle position sensor output not charging (indicating a steady road speed), transmission 3rd gear switch closed, and brake switch closed.

1. Light off confirms transmission 3rd gear apply switch is open.
2. At 30 MPH transmission/transaxle 3rd gear switch should close. Test light will come on and confirm battery supply and closed brake switch.
3. Grounding diagnostic terminal with engine off should energize TCC solenoid. This test checks capability of ECM to control solenoid.
4. Solenoids are turned on or off by ECM internal electronic switches called drivers. Each driver is part of a group of 4 called QuaDDrivers. Failure of one can damage another driver within a set. Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure of ECM driver. Using an ohmmeter, check solenoid coil resistance before installing a replacement ECM.

Check TCC solenoid resistance. Disconnect TCC at transmission. Connect ohmmeter between transmission connector opposite harness connector terminal A and D. Raise drive wheels. Run engine in drive about 30 MPH to close 3rd gear apply switch. Replace TCC solenoid and ECM if resistance measures less than 20 ohms when switch is closed.

Flow Chart C8: 125C TCC. Scheme 281

Flow Chart C8: 125C TCC. Scheme 282

Chart C8 Schematic: 125C TCC. Scheme 283

CHART C8A - 700-4R TCC (F BODY)

The purpose of automatic transmission/transaxle 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/transaxle and fuel economy of a manual transmission. Fused battery ignition is supplied to TCC solenoid through brake switch, and transmission 3rd gear apply switch. The ECM will engages TCC by grounding circuit No. 422 to energize solenoid.

TCC will engage when vehicle speed is above 20-22 MPH, engine at normal operating temperature (above 158°F/70°C), throttle position sensor output not charging (indicating a steady road speed), transmission 3rd gear switch closed, and brake switch closed.

1. Checks continuity through brake switch, TCC solenoid, and 4-3 downshift switch.
2. Checks capability of ECM to energize solenoid. Grounding diagnostic connector should energize relay and cause light to go out.
3. This test bypasses TCC solenoid and 4-3 switch and checks for an open or short in circuit No. 422.
4. Solenoids are turned on or off by ECM internal electronic switches called drivers. Each driver is part of a group of 4 called QuaDDrivers. Failure of one can damage another driver within a set. Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure of ECM driver. Using an ohmmeter, check solenoid coil resistance before installing a replacement ECM.

Flow Chart C8A: 700-4R TCC (F Body). Scheme 284

Flow Chart C8A: 700-4R TCC (F Body). Scheme 285

Chart C8A Schematic: 700-4R TCC (F Body). Scheme 286

CHART C8B - M/T SHIFT LIGHT (F BODY)

The shift light indicates best transmission shift point for maximum fuel economy. The light is controlled by ECM and is turned on by grounding terminal 19 circuit No. 456. The ECM uses MAP, distributor reference (engine speed), VSS and coolant temperature information for control.

Flow Chart C8B: M/T Shift Light (F Body). Scheme 287

Flow Chart C8B: M/T Shift Light (F Body). Scheme 288

CHART C9 - 2.5L M/T SHIFT LIGHT (J/N/P BODY)

The shift light indicates best transmission shift point for maximum fuel economy. The light is controlled by ECM and is turned on by grounding terminal 19 circuit No. 456. The ECM uses MAP, distributor reference (engine speed), VSS and coolant temperature information for control. The ECM uses measured RPM and vehicle speed to calculate what gear vehicle is in. It's this calculation that determines when shift light should be turned on.

1. This should not turn on shift light. If light is on, there is a short to ground in circuit No. 456 wiring or a fault in ECM.
2. When diagnostic terminal is grounded, the ECM should ground circuit No. 456 and shift light should come on.
3. This checks shift light circuit up to ECM connector. If shift light illuminates, then ECM connector is faulty or ECM does not have ability to ground circuit.

Flow Chart C9: 2.5L M/T Shift Light (J/N/P Body). Scheme 289

Flow Chart C9: 2.5L M/T Shift Light (J/N/P Body). Scheme 290

CHART C10 - 2.5L A/C CLUTCH CONTROL (A/F BODY)

ECM control of A/C clutch improves idle quality and performance by delaying clutch apply until idle air rate is increased, releasing clutch when idle speed is too low, releasing clutch at wide open throttle, and smooths cycling of compressor by providing additional fuel at instant clutch is applied. Turning on air conditioning supplies circuit No. 459 battery voltage to clutch control relay and terminal 21 of White ECM connector. After time delay of about 1/2 seconds, ECM will ground terminal 7 of Black ECM connector circuit No. 458 and close control relay.

1. Checks for low refrigerant as cause for no A/C.
2. This and following tests check for faulty A/C control relay.
3. Checks for faulty cycling switch. Solenoids and relays are turned on or off by ECM, using internal electronic switches called drivers. Each driver is part of a group of 4 called QuaDDrivers. Failure of one driver can damage another driver in a set. Solenoid and relay coil resistance must measure more than 20 ohms. Less resistance will cause early failure of ECM driver. Using an ohmmeter, check coil resistance of A/C relay before replacing ECM.

Flow Chart C10: A/C Clutch Control (1 Of 2) (2.5L A/F Body). Scheme 291

Flow Chart C10: A/C Clutch Control (1 Of 2) (2.5L A/F Body). Scheme 292

Flow Chart C10: A/C Clutch Control (2 Of 2) (2.5L A/F Body). Scheme 293

Flow Chart. Scheme 294

Chart C10 Schematic: A/C Clutch Control. Scheme 295

CHART C10 - 2.5L A/C CLUTCH CONTROL (P BODY)

ECM control of A/C clutch improves idle quality and performance by delaying clutch apply until idle air rate is increased, releasing clutch when idle speed is too low, releasing clutch at wide open throttle, and smooths cycling of compressor by providing additional fuel at instant clutch is applied.

Voltage is supplied to A/C clutch control relay on circuit No. 50 as A/C power relay is energized by A/C control switch. At same time, voltage is supplied to A/C relay coil on circuit No. 67 and as a signal to ECM pin 21 (White connector). After a time delay of about 1/2 seconds, ECM will ground terminal 7 of Black connector circuit No. 458 and close A/C relay. When relay is energized, battery voltage from circuit No. 50 is supplied to A/C clutch through relay and circuit No. 59.

Flow Chart C10: A/C Clutch Control (2.5L P Body). Scheme 296

Flow Chart C10: A/C Clutch Control (2.5L P Body). Scheme 297

Chart C10 Schematic: A/C Clutch Control (2.5L P Body). Scheme 298

CHART C10A - A/C CLUTCH CONTROL (J/N BODY)

With air conditioning on, ignition voltage is supplied to compressor high side low pressure switch (identified by its Black color). If system refrigerant level is okay, low pressure switch will be closed completing circuit through closed high pressure cutoff switch (Red color) to circuit No. 459.

Circuit No. 459 supplied voltage to A/C control relay and ECM terminal 21. The ECM will delay about 1/2 seconds, then ground terminal 7 and circuit No. 458. This will close A/C relay and allow current to flow through relay and circuit No. 59 to engage compressor clutch.

Flow Chart C10A: A/C Clutch Control (J/N Body). Scheme 299

Flow Chart C10A: A/C Clutch Control (J/N Body). Scheme 300

Chart C10A Schematic: A/C Clutch Control (J/N Body). Scheme 301

CHART C12 - 2.5L ENGINE COOLING FAN (A BODY)

Battery voltage is supplied to fan relay on terminal E and ignition to terminal C. Grounding relay terminal B will close relay and supply battery voltage to fan motor. Above 30 MPH, the ECM will remove ground from circuit No. 409. If coolant temperature and A/C pressure switches are open, fan will stop.

Flow Chart C12: Engine Cooling Fan (2.5L A Body). Scheme 302

Flow Chart C12: Engine Cooling Fan (2.5L A Body)(1 Of 2). Scheme 303

Flow Chart C12: Engine Cooling Fan (2.5L A Body)(2 Of 2). Scheme 304

Chart C12 Schematic: Engine Cooling Fan (2.5L A Body). Scheme 305

CHART C12A - ENGINE COOLING FAN (J/N BODY)

Battery voltage is supplied to fan control relay terminal E and ignition terminal C. Grounding circuit No. 335 will close relay and is controlled by fan temperature switch when A/C is off or vehicle speed is above 30 MPH. When A/C control switch is on and compressor high side low pressure switch is closed, circuit No. 901 will provide ignition voltage to terminal A of A/C fan relay.

If vehicle speed is less than 30 MPH, ECM terminal 9 and circuit No. 409 are grounded. The A/C fan relay coil is grounded closing relay which in turn grounds circuit No. 335.

Flow Chart C12A: Cooling Fan (1 of 2) (J/N Body). Scheme 306

Flow Chart C12A: Cooling Fan (1 Of 2) (J/N Body). Scheme 307

Flow Chart C12A: Cooling Fan (2 of 2) (J/N Body). Scheme 308

Flow Chart C12A: Cooling Fan (2 Of 2) (J/N Body). Scheme 309

Chart C12A Schematic: Engine Cooling Fan (J/N Body). Scheme 310

Component Locations (A/N Body 2.5L). Scheme 311

Component Locations (F/P Body 2.5L). Scheme 312

ECM Terminal ID & Pin Voltage (A/F/N Body 2.5L). Scheme 313

ECM Terminal ID & Pin Voltage (P Body 2.5L). Scheme 314

CCC Wiring Diagram (1.8L & 2.5L Engines). Scheme 315