Diagnosis - Torque Converter Clutch GMC Pickup R2500

DESCRIPTION

Note. This article contains test charts that are part of General Motors Computerized Engine Controls. Only those charts required to test Torque Converter Clutch (TCC) system and related circuits are included. Other diagnostic codes may appear while performing TCC electrical diagnosis. For complete information on General Motors Computerized Engine Control systems see appropriate article in ENGINE PERFORMANCE.

The Torque Converter Clutch (TCC) assembly consists of a 3-element torque converter with the addition of a converter clutch. The converter clutch is an internal mechanism with friction material attached to front face. It is splined to the turbine assembly in converter.

The purpose of the torque converter clutch feature is to eliminate power loss due to slippage when vehicle is cruising. This allows the convenience of an automatic transmission and the fuel economy of a manual transmission.

When the TCC solenoid ground circuit is completed by the Electronic Control Module (ECM), the torque converter clutch is applied, resulting in a direct mechanical coupling between engine and transmission. When TCC solenoid is deactivated, the torque converter clutch is released, allowing torque converter clutch to operate in a conventional manner.

Scheme 92

TCC CONTROL COMPONENTS

The following components are used to engage/disengage torque converter clutch. Not all components will be present on all vehicles.

Brake Switch

Power from ignition switch passes through brake switch to TCC solenoid. When brake pedal is depressed with TCC engaged, power to TCC solenoid is interrupted, releasing converter clutch and preventing engine from stalling.

Coolant Temperature Sensor

This sensor provides ECM with engine coolant temperature information. ECM will not allow TCC operation until signal from this sensor indicates coolant temperature greater than 130°-150°F (55°-65°C).

Electronic Control Module (ECM)

To determine application of torque converter clutch, ECM receives and processes information from various input devices. On the most sophisticated vehicles, these devices may include the vehicle speed sensor, coolant temperature sensor, throttle position sensor, 3rd or 4th gear switch and brake switch. The ECM controls application of torque converter clutch by providing a ground circuit for the TCC solenoid circuit.

TCC Solenoid Assembly

Energized by ECM to redirect transaxle fluid to the converter clutch apply valve in the auxiliary control valve assembly.

Throttle Position Sensor (TPS)

Provides ECM with throttle position information. TCC operation is prevented when throttle position signal is less than a specified value.

Vacuum Sensor

Sends engine vacuum (load) information to ECM.

Vehicle Speed Sensor (VSS)

This sensor sends vehicle speed information to ECM. Vehicle speed must be greater than a certain value before TCC can be applied. Two types of speed sensor are used. A light emitting diode type is used in the instrument cluster on some models. Other models use a Permanent Magnet (PM) generator mounted in the transmission.

3rd & 4th Gear Switch

When open, 3rd and 4th gear switches prevent TCC operation. Switch status may be monitored by ECM, or switch may be an integral portion (series circuit) of TCC solenoid power supply.

TROUBLE SHOOTING

Note. Every diagnosis of automatic transmission problems should begin with a check of the transmission fluid and linkage. Most of the following conditions can be caused by one or more of the following factors: (1) Incorrect fluid level, (2) Contaminated fluid, (3) Improperly adjusted linkage, or (4) Damaged or worn linkage. When diagnosing Converter Clutch problems, ensure engine and vacuum systems are in perfect operating order.

Problem in Electronic Control Module

1. Verify Electronic Control Module (ECM) operation. See appropriate CHART C-8 in this article.

Electrical Problems

1. Voltage not reaching transmission. Ensure 12 volts reach transmission to engage solenoid.
2. Ground inside transmission. Ensure solenoid is not grounded inside case.
3. Defective connector, wiring harness, or solenoid. Check and repair or replace as required. Defective pressure switch (if equipped). Check and replace pressure switch as required.
4. 3rd and/or 4th gear switch inoperative. Check and replace switch(es) as required.

Valve Body Assembly

1. Sticking converter clutch shift and/or apply valve. Clean, service and/or replace valve body as required.
2. Sticking throttle valve. Clean, service and/or replace valve body as required.
3. No. 10 check ball missing (THM 440-T4). Inspect valve body and service as required.

Oil Pump Assembly

1. Orifice plugged for converter signal oil in pump. Clean and inspect orifice for blockage.
2. Solenoid "O" ring damaged or missing. Check and replace "O" ring.
3. Oil pump wear plate or gasket mispositioned or damaged. Check and replace wear plate or gasket.
4. Improper torque on oil pump-to-converter housing bolts. Tighten bolts to specifications.
5. Turbine shaft seals damaged. Check and replace seals.
6. Orifice cup plug omitted from cooler in passage. Check and install plug.
7. Channel plate (THM 440-T4). Check and replace converter clutch blow-off check ball if not seated or if damaged. Check and replace torque converter clutch accumulator piston or seal if damaged.

CONVERTER CLUTCH APPLY SLIPPING, ROUGH OR SHUDDERS

1. Converter clutch pressure plate faulty. Check plate for damage and service as required.
2. Damaged or missing check ball in end of turbine shaft. Check and replace turbine shaft, if required.
3. Converter clutch regulator valve stuck. Clean, service and/or replace valve body as required.
4. Converter clutch accumulator piston or seal damaged. Check and service as required.
5. Channel plate spring damaged (THM 440-T4). Replace channel plate.
6. Incorrect converter clutch blow-off spring installed (THM 440-T4). Check and install correct spring.
7. Channel plate seals damaged or missing. Check and service as required.
8. Turbine shaft seals damaged or missing (THM 440-T4). Check and replace turbine shaft seals or shaft.

CONVERTER CLUTCH DOES NOT RELEASE

1. Solenoid does not exhaust. Verify Electronic Control Module operation. See appropriate CHART C-8 in this article.
2. Converter clutch apply valve stuck. Clean, service and/or replace valve body as required.
3. Check damaged converter. Replace torque converter.
4. Cup plug missing from pump release passage. Check and replace plug or pump assembly.
5. Turbine shaft end seal damaged or missing. Check and replace end seal or turbine shaft as required.
6. Hole not drilled through turbine shaft. Replace turbine shaft.

DIAGNOSTIC TOOLS

Note. In the diagnostic and trouble code charts, special "Scan" testers are referred to (and recommended) by the manufacturer to read data parameters and check voltages in the system.

Diagnosis of the TCC system may be performed by following the appropriate C-8 chart for the transmission/engine application in question. When utilizing these charts, specific tools which may be required are a tachometer, test light, ohmmeter, digital voltmeter with 10-megohm input impedance (minimum), 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). A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart(s).

RETRIEVING TROUBLE CODES

Note. Even when using a "Scan" tester, it is recommended that the diagnostic mode be accessed in advance to verify the computer's ability to self-diagnose.

The ECM stores component failure information under a related trouble code which can be recalled later for diagnosis and repair. When recalled, these codes can be displayed on a "Scan" tester, or by entering diagnostic mode and observing flashes of the "CHECK ENGINE" or "SERVICE ENGINE SOON" light. It is NOT necessary to enter diagnostic mode to use TCC test chart(s); however, it will be necessary to enter ECM diagnostic mode to verify the presence of any codes.

Entering ECM Diagnostic Mode

Note. If Code 12 is not flashed when the ALCL diagnostic "test" terminal is grounded, information received by a "Scan" tester on the serial data line may not be accurate. For complete testing of the ECM's diagnostic circuit, refer to appropriate article in ENGINE PERFORMANCE.

Scheme 93

1. To enter diagnostic mode, turn ignition on but do not start engine. "CHECK ENGINE" or "SERVICE ENGINE SOON" light should glow. Locate Assembly Line Communication Link (ALCL) connector attached to ECM wiring harness under instrument panel (in center console on Fiero). Insert jumper wire across diagnostic mode "test" terminal "B" and ground terminal "A". (Scheme 93)
2. "CHECK ENGINE" or "SERVICE ENGINE SOON" light should flash Code 12 ("FLASH", pause, "FLASH", "FLASH") followed by a longer pause. Trouble Code 12 will be repeated 3 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 ALCL connector is grounded.
4. To exit diagnostic mode, remove jumper wire from ALCL connector and turn ignition off.

CLEARING TROUBLE CODES

Trouble codes are cleared by removing battery voltage from ECM for at least 10 seconds. Ensure that "test" terminal is not grounded. Turn ignition off and remove ECM fuse from fuse block for 10 seconds and then reinsert it. Another way of removing battery voltage is to disconnect the battery positive cable (or pigtail) from the battery for 10 seconds and then reconnect it. In either case, ensure the ignition switch is in the "OFF" position before removing battery voltage. Otherwise, a voltage spike could occur and damage the ECM.

The TCC system does not require special tools for diagnosis. A tachometer, a test light, ohmmeter, digital voltmeter with 10-megohm input impedance (minimum), 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. A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart(s). Since the digital dash on these systems is used to access data parameters, no special equipment is required.

ENTERING SERVICE (DIAGNOSTIC) MODE

Note. Operating vehicle in service mode for extended periods of time without engine running will cause the battery to run down and possibly relate false diagnostic information. Connect battery charger on "trickle" charge if vehicle is to be in service mode for periods longer than 1/2 hour.

It will be necessary to enter service mode to use Reatta, Riviera and Toronado TCC test chart(s). Enter appropriate test condition (i.e. ECM INPUTS, BCM CODE, etc.) as indicated in chart(s).

1. On Reatta and Riviera, turn ignition on. Simultaneously touch the "OFF" and "WARM" key pads on the Cathode Ray Tube (CRT) "climate control" page. Hold until a double "beep" is heard or a page entitled "SERVICE MODE" appears on the screen. (Scheme 94)and (Scheme 95).
2. On Toronado, turn ignition on. Simultaneously depress the "OFF" and "WARM" buttons on the Electronic Climate Control (ECC) panel. Hold (about 3 seconds) until a segment check is displayed on the Instrument Panel Cluster (IPC) and ECC panel. (Scheme 96)

Scheme 94

Scheme 95

Scheme 96

Reatta & Riviera

After service mode is entered any trouble codes stored in the computer memory will be displayed. Codes will also be accompanied by "Current" or "History". "History" indicates that the failure was not present when last tested. "Current" indicates the fault still exists. ECM codes will be displayed first. If no ECM codes are stored, the CRT will display "NO ECM CODES" for approximately 2 seconds.

After ECM codes have been displayed, the Body Control Module (BCM) codes will be displayed. BCM codes mainly deal with body control functions, with climate control being one of its main features. If no BCM codes are present, the BCM will display "NO BCM CODES" message. Trouble codes for both the ECM and BCM will be displayed in numerical succession of lowest to highest numbered code.

After BCM codes have been displayed, CRT codes will be displayed for approximately 2 seconds each. All CRT codes will be prefixed with a "C". The lowest will be displayed first. If there are no CRT codes stored, "NO CRT CODES" will be displayed.

If the "NO" pad is touched any time during display, display of codes will be by-passed. If the "EXIT" pad is touched at any time during the display of trouble codes, ECM will exit "Service Mode" and go back to normal vehicle operation.

Toronado

After service mode is entered, any trouble codes stored in the computer will be displayed. Codes will also be accompanied by "Current" or "History". "History" indicates that the failure was not present when last tested. "Current" indicates the fault still exists. ECM codes will be displayed first. If no ECM codes are stored, the IPC will display "NO ECM CODES". All ECM codes will be prefixed by an "E" (i.e. E013).

When all ECM codes have been displayed, the Body Control Module (BCM) codes will be displayed. BCM codes mainly deal with body control functions, with climate control being one of its main features. BCM codes are prefixed with an "B" (i.e. B110). If no BCM codes exist, "NO BCM CODES" message will be displayed.

Both ECM and BCM codes are displayed in 2 second intervals starting at the lowest numbered code and ending at the highest. If the "LO" fan button is pressed anytime during the display of ECM and BCM codes, the display of codes will be by-passed. If at any time the "BI-LEV" button is pressed, the BCM will exit the service mode and go back to normal vehicle operation.

ECM & BCM TROUBLE CODES

After trouble codes have been displayed, the service mode can be used to perform several tests on different systems one at a time. Upon completion of the trouble code display, a specific system may be selected for testing. Following the trouble code display, the first available system will be displayed (i.e. ECM). When making system selections there are 3 available alternatives

1. Pressing the "EXIT" key pad will stop the system selection process and return to the beginning of the trouble code sequence.
2. Pressing the "NO" key pad will display the next available system selection.
3. Pressing the "YES" key pad will select the displayed system for testing.

After trouble codes have been displayed, the service mode can be used to perform several tests on different systems one at a time. Upon completion of trouble code display, a specific system may be selected for testing. Following trouble code display, the first available system will be displayed (i.e. ECM). When selecting a test, there are 4 available actions to be taken

1. Pressing the "OFF" button will stop the system selection process and return the display to the beginning of the trouble code sequence.
2. Pressing the "LO" fan button will display the next available system selection. This allows all system selections to be displayed.
3. Pressing the "HI" fan button will select the displayed system for testing.
4. Pressing the "BI-LEV" button will exit diagnostics and return to normal IPC and ECC operation.

Having selected a system, the first available test type will be displayed (i.e. "ECM DATA"). When making selection of test type there are 3 available alternatives

1. Pressing the "EXIT" key pad will stop the test type selection and return the display to the next available system selection.
2. Pressing the "NO" key pad will display the next available test type for the selected system. This allows the display to be stepped through all available test type choices.
3. Pressing the "YES" key pad will select the displayed test type. Here, the display will either indicate that the selected test type is in progress or the first of several specific tests will appear. If "NO DEVICES" appears, no test is available.

Having selected a system, the first available test type will be displayed (i.e. "ECM DATA"). When selecting a specific test type there are 4 available actions to be taken

1. Pressing the "OFF" button will stop the test type selection process and return to the next available selection.
2. Pressing the "LO" fan button will display the next available test type for the selected system. This allows all available test types to be displayed for selection.
3. Pressing the "HI" fan button will select the displayed test type. Here the display will either indicate whether the selected test type is in progress or the first of several tests will appear.
4. Pressing the "BI-LEV" button will exit diagnostics.

Selection of "DATA", "INPUTS", "OUTPUTS", or "OVERRIDE" test types will result in the first available test being displayed. If a "Select ERR" message appears, this test is not allowed with the engine running. Turn engine off and try again.

Four characters of the display will contain a test code to identify the selection. The first 2 characters are letters which identify the system and test type (i.e. "ED" for "ECM DATA"), while the last 2 characters numerically identify the test. When selecting these tests, 3 alternatives are available

1. Pressing the "EXIT" key pad will stop the test selection process and return the display to the next test type for the selected system.
2. Pressing the "NO" key pad will display the next smaller test number. If the lowest number is already displayed, the highest number will then be displayed.
3. Pressing the "YES" key pad will display the next larger test number for the selected test type. If the highest number is already displayed, the lowest number will appear.

Scheme 97

Selection of "DATA", "INPUTS", or "OUTPUTS" test types will result in the first available test being displayed. If the message, "EEEE" appears it means that test is not allowed with the engine running. Turn engine off and repeat sequence.

The last 4 characters of the display will contain a test code to identify the selection. The first 2 of these characters are letters which identify the system and the test type (i.e. "ED" for "ECM DATA"), while the last 2 characters numerically identify the test. When selecting a specific test there are 3 available actions to be taken

1. Pressing the "OFF" button will stop the test selection process and return the display to the next available test type for the selected system.
2. Pressing the "LO" fan button will display the next smaller test number for the selected test type.
3. Pressing the "HI" fan button will display the next larger test number for the selected test type.

Scheme 98

Upon selection of an "OVERRIDE" test function, current operation will be represented as a percentage of its full range. This value will be displayed on the ECC panel. The display will alternate between "--" and the normal program value. This alternating display is a reminder that the function is not currently being overridden.

Pressing the "WARM" or "COOL" buttons on the ECC panel begins the override, at which time the display will no longer alternate. Pressing the "WARM" button increases the value while pressing the "COOL" button decreases the value. Normal program control can be resumed in 1 of 3 ways

1. Selection of another override test will cancel the current override.
2. Selection of another system (i.e. ECM, BCM) will cancel the current override.
3. Overriding the value beyond either extreme (0 or 99) will display "--" momentarily and then jump to the opposite extreme. If the button is released while "--" is being displayed, normal program control will resume and the display will again alternate.

The override test type is unique in that any other test type within the selected system may be active at the same time. After selecting an override test, pressing the "OFF" button will allow selection of another test type, "DATA", "INPUTS" or "OUTPUTS". The ECC panel will continue to display the selected override. By selecting another test type and test, while at the same time pressing the "WARM" or "COOL" button, it is possible to monitor the effect of the override on different vehicle parameters.

Selection of "CLEAR CODES?" test type will result in the message "CODES CLEAR" being displayed with the selected system name above it after the "YES" pad has been touched. This message appears for 3 seconds to indicate that all stored trouble codes have been erased from memory. After this 3-second interval, the system will automatically return to the next available test type for the selected system.

Selecting "CLEAR CODES" option will result in the message "CLEAR ECM CODES?" or "CLEAR BCM CODES?" being displayed, depending on which system was being tested. At this time, the following action may be taken

1. Pressing the "OFF" button will stop the test selection process and return the display to the next available test type for the selected system.
2. Pressing the "LO" fan button will display the next test type.
3. Pressing the "HI" fan button will select "CLEAR CODES". A message "ECM CODES CLEARED" or "BCM CODES CLEARED" will appear to indicate those codes have been cleared from memory.
4. Pressing the "BI-LEV" button will exit diagnostics.

To exit service mode, turn ignition off or repeatedly press the "EXIT" key pad until the "SERVICE MODE" page disappears. Trouble codes are not erased when this is done.

To exit service mode, press the "BI-LEV" button. Trouble codes are not erased when this is done. Any mode button will exit diagnostics; however, the "BI-LEV" button was chosen for consistency.

DATA DISPLAYS

When trouble shooting a malfunction, the ECM and BCM data display can be used to compare the vehicle with problems, with a vehicle that is functioning properly. When ECM data "ED12" or BCM data "BD60" is entered, vehicle speed is displayed from "0" (zero) to "159" MPH.

ECM DATA & BCM DATA DISPLAY CODES

INPUT DISPLAYS

When trouble shooting a malfunction, the ECM, BCM, or IPC input display can be used to determine if the switched inputs are properly interpreted. When one of the input tests is selected, the state of that device is displayed as "HI" or "LO". Basically, "HI" or "LO" represent the input terminal voltage for that circuit.

The display also indicates if the input changed state since it was last tested. If a change occurred, an "X" will appear next to the "HI"/"LO" indicator. On Reatta and Riviera, if a change did not occur, a "O" will remain displayed. The "X" will only appear once per selected input. When input display "E182" is entered, the 4th gear switch is "HI" when vehicle is in 4th gear.

ECM INPUT DISPLAY CODE

OUTPUT DISPLAYS

When trouble shooting a malfunction, the ECM and BCM output cycling can be used to determine if output tests can be actuated regardless of the inputs and normal program instructions. Once a test in outputs is selected, except for ECM IAC, the test will display "HI" or "LO" for 3 seconds in each state to indicate the command and output terminal voltage. When ECM output "EO01" is entered, the torque converter clutch display will be "LO" when TCC is on (energized.)

ECM OUTPUT DISPLAY CODE

TCC DIAGNOSTIC CHARTS

Use the following diagnostic charts to diagnose the TCC electrical system. Make sure to use appropriate test charts. Using wrong test charts will result in TCC misdiagnosis. Some test steps may refer you to corresponding vehicle speed sensor (Code 24) and park/neutral switch test charts.

Note. The following component and trouble code charts are furnished courtesy of General Motors Corp.

CHART C-8, TORQUE CONVERTER CLUTCH - CARBURETED PASSENGER CARS (1 AND 2 OF 3)

Fused battery ignition is supplied to TCC solenoid through the brake switch. The ECM will engage TCC by grounding circuit No. 422 to energize solenoid. TCC will engage when

1. Vehicle speed is greater than 24 mph.
2. Engine is at operating temperatures greater than 156°F (70°C).
3. Throttle position sensor not changing (indicating steady road speed).
4. Brake switch closed. NOTE: Test numbers refer to test numbers on diagnostic chart. This test confirms a 12-volt supply as well as continuity of TCC circuit. When ALDL "test" terminal is grounded with engine off, ECM capability is energized to control the solenoid. Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause continual opening of ECM "quad driver". Using an ohmmeter, check solenoid coil resistance of all ECM-controlled solenoids and relays. Replace any solenoid or relay that measures less than 20 ohms.

Diagnostic Aids

An engine coolant thermostat that is stuck open or opens at too low a temperature, may result in an inoperative TCC. On 200-4R transmission, if TCC engages before "Scan" tester indicates TCC "ON", wiring may be grounded between TCC solenoid and sump over temperature switch or switch may be faulty.

Flow Chart C8, TCC Elect. Check Flow Chart 5.0/5.7L (1 of 2). Scheme 99

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

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

Chart C-8, Torque Converter Clutch - Carbureted Passenger Cars (1 Of 2). Scheme 100

Chart C-8, Torque Converter Clutch - Carbureted Passenger Cars (2 Of 3). Scheme 101

CHART C-8, TORQUE CONVERTER CLUTCH - CARBURETED PASSENGER CARS (3 OF 3)

On 700-4R transmission, a 4th gear switch (mounted in the transmission) opens when transmission shifts into 4th gear. This switch is used by ECM to modify TCC lock and unlock points, when in a 4th-to-3rd downshift maneuver.

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

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

If "Scan" tester indicates TCC is turning on and off erratically, check the state of the 4th gear switch to be sure it is not changing states under a steady throttle position. If switch is changing states, check connections and wire routing carefully. Also if the 4th gear switch is always open, TCC may engage as soon as sufficient oil pressure is reached.

Flow Chart C8, TCC 700-4R Electrical Check, 5.0/5.7L (2 Of 2). Scheme 102

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

Chart C-8, Torque Converter Clutch - Carbureted Passenger Cars (3 Of 3). Scheme 103

CODE 24, VEHICLE SPEED SENSOR - CARBURETED PASSENGER CARS

The ECM applies and monitors 12 volts on circuit No. 437 to Vehicle Speed Sensor (VSS). VSS alternately opens and grounds circuit No. 437 when drive wheels are turning. This pulsing action takes place about 2000 times per mile and ECM calculates vehicle speed based on time between pulses. "Scan" tester reading should closely match speedometer reading.

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

1. This test monitors ECM voltage on circuit No. 437. With drive wheels turning, pulsing action varies voltage. This variation is greater at low speeds to an average of 4-6 volts at about 20 mph (32 km/h). Cruise control must be off for accurate test results.
2. This test checks for a grounded circuit. A voltage of less than one volt indicates that circuit No. 437 is shorted to ground. Disconnect circuit No. 437 at VSS. The VSS is faulty if voltage now reads more than 10 volts. If voltage remains less than one volt, circuit No. 437 is grounded. If circuit is not grounded, check for a 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 is a normal voltage condition and indicates a possible intermittent condition.
5. This step will isolate whether problem is in circuit No. 437 or ECM.

Code 24, Vehicle Speed Sensor Flow Chart. Scheme 104

Note. To prevent misdiagnosis, the technician should review electrical section or electrical troubleshooting manual and identify the type of vehicle speed sensor used prior to using this chart. Disregard Code 24, if set when drive wheels are turning.

Code 24, Vehicle Speed Sensor - Carbureted Passenger Cars. Scheme 105

CHART C-8, TORQUE CONVERTER CLUTCH 2.0L & 2.5L TBI - A, J, N & P BODIES

The purpose of the automatic transmission/transaxle Torque Converter Clutch (TCC) feature is to eliminate power loss of torque converter stage when vehicle is in a 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 a brake switch, and transmission 3rd gear apply switch. The ECM will engage TCC by grounding circuit No. 422 to energize solenoid.

TCC will engage when vehicle speed is greater than 30 MPH, engine at normal operating temperature (greater than 158°F/70°C), throttle position sensor output not changing (indicating a steady road speed), transmission 3rd gear switch closed, and brake switch closed.

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

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 by grounding circuit No. 422. This test checks capability of ECM to control solenoid.

A thermostat that is stuck in the open position, or opens at too low a temperature, may result in an inoperative TCC.

Note. ECM terminal B7 on early L Body is F6.

Chart C-8A: Trans Converter Clutch Flow Chart. Scheme 106

Note. DO NOT perform this test without supporting the lower control arms so that the drive axles are in a normal horizontal position. Running the vehicle in gear with the wheels hanging down at full travel may damage the drive axles.

Chart C-8, Torque Converter Clutch 2.0L & 2.5L TBI - A, J, N & P Bodies. Scheme 107

Chart C-8A: Trans Converter Clutch Ckt Diag. Scheme 108

CODE 24, VEHICLE SPEED SENSOR 2.0L & 2.5L TBI - A, J & N BODIES (WITH PM GENERATOR)

The speed sensor, which is a Permanent Magnet (PM) generator, provides the ECM with vehicle speed information. The PM generator, mounted in the transmission, produces a pulsing voltage signal whenever the vehicle speed is over 3 MPH. The voltage level and the number of pulses increase with vehicle speed. The ECM converts the pulsing voltage to MPH, which is used by the ECM in calculations to determine vehicle adjustments.

A Code 24 will set when MPH reads zero, transmission is not in Park or Neutral, engine speed is between 1400-4400 RPM, TPS is at 2 percent (closed throttle), and a high manifold vacuum is sensed by the MAP sensor. All of these conditions must be met for 3-5 seconds.

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

1. This test monitors the ECM voltage on circuit No. 993. With wheels turning, the pulsating action created in circuits No. 400 and 401 will result in a voltage signal to the ECM and be displayed as MPH. The PM generator only produces a voltage signal if drive wheels are turning greater than 3 MPH.
2. Before replacing the ECM PROM should be checked for correct application.

A faulty or misadjusted Park/Neutral switch may set a false Code 24. Use "Scan" tester and check for proper signal in Drive, while wiggling shifter.

Code 24 Schematic: VSS (A/J/N Body) (VSS W/P.M. Generator). Scheme 109

Flow Chart, Code 24: VSS (A/J/N Body) (VSS W/P.M. Generator). Scheme 110

Note. DO NOT perform this test without supporting the lower control arms so that the drive axles are in a normal horizontal position. Running the vehicle in gear with the wheels hanging down at full travel may damage the drive axles.

Code 24, Vehicle Speed Sensor 2.0L & 2.5L TBI - A, J & N Bodies (With PM Generator). Scheme 111

CODE 24, VEHICLE SPEED SENSOR 2.5L TBI - A BODY (WITH IN-DASH SPEED SENSOR)

The ECM applies and monitors a 12-volt signal on circuit No. 437. Circuit No. 437 connects to the vehicle speed sensor and is alternately grounded when the wheels are turning. The pulsing action takes place approximately 2000 times per mile and the ECM will calculate vehicle speed based on the time between pulses.

Code 24 will set if vehicle speed reads zero MPH, transmission is not in Park or Neutral, engine speed is between 1400-4400 RPM, TPS is less than 2 percent, a high manifold vacuum is sensed by the MAP sensor, and these conditions have existed for more than 5 seconds.

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

1. ECM monitors circuit No. 437, counting voltage pulses created by the grounding of the speed sensor. "Scan" reading should closely match speedometer reading with drive wheels turning.
2. 8-12 volts at the I. P. connector indicates circuit No.437 is open or there is a faulty speed sensor. A voltage of less than one volt at I. P. connector indicates that circuit No. 437 wire is shorted to ground or open between the connector and the ECM. The I.P. connector is located in the center console near the ECM.

A faulty or misadjusted Park/Neutral switch may set a false Code 24. Use "Scan" tester and check for proper signal in Drive, while wiggling shifter.

Flow Chart & Schematic, Code 24: VSS W/In-Dash Speed Sensor (A Body). Scheme 112

Note. DO NOT perform this test without supporting the lower control arms so that the drive axles are in a normal horizontal position. Running the vehicle in gear with the wheels hanging down at full travel may damage the drive axles.

Code 24, Vehicle Speed Sensor 2.5L TBI - A Body (With In-Dash Speed Sensor). Scheme 113

CODE 24, VEHICLE SPEED SENSOR 2.5L TBI - P BODY

The ECM applies and monitors a 12-volt signal on circuit No. 389. Circuit No. 389 connects to the vehicle speed sensor and is alternately grounded when the wheels are turning. The pulsing action takes place approximately 2000 times per mile and the ECM will calculate vehicle speed based on the time between pulses.

Code 24 will set if vehicle speed reads zero MPH, transmission is not in Park or Neutral, engine speed is between 1400-3600 RPM, TPS is less than 2 percent, a low load (air flow) rate is sensed and these conditions have existed for more than 5 seconds.

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

1. ECM monitors circuit No. 389, counting voltage pulses created by the grounding of the speed sensor. "Scan" reading should closely match speedometer reading with drive wheels turning.
2. 8-12 volts at the I. P. connector indicates circuit No. 389 is open or there is a faulty speed sensor. A voltage of less than one volt at I. P. connector indicates that circuit No. 389 wire is shorted to ground or open between the connector and the ECM. The I.P. connector is located in the center console near the ECM.

A faulty or misadjusted Park/Neutral switch may set a false Code 24. Use "Scan" tester and check for proper signal in Drive, while wiggling shifter.

Flow Chart & Schematic, Code 24: VSS (P Body). Scheme 114

Note. DO NOT perform this test without supporting the lower control arms so that the drive axles are in a normal horizontal position. Running the vehicle in gear with the wheels hanging down at full travel may damage the drive axles.

Code 24, Vehicle Speed Sensor 2.5L TBI - P Body. Scheme 115

CHART C-1A, PARK/NEUTRAL SWITCH 2.0L & 2.5L TBI - A, J, N & P BODIES

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 volt. The ECM uses this signal as one of the inputs to control IAC and VSS diagnostics.

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

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. Be sure "Scan" tester indicates Drive. Wiggle shifter to test for an intermittent or misadjusted switch.

Chart C1A Schematic: Park/Neutral Switch A/T (A/J/N/P Body). Scheme 116

Flow Chart C1A: Park/Neutral Switch A/T (A/J/N/P Body). Scheme 117

Chart C-1A, Park/Neutral Switch 2.0L & 2.5L TBI - A, J, N & P Bodies. Scheme 118

CHART C-8, TORQUE CONVERTER CLUTCH 2.0L (VIN 1) TBI - J & L BODIES

The purpose of the automatic transmission/transaxle Torque Converter Clutch (TCC) feature is to eliminate power loss of torque converter stage when vehicle is in a 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 a brake switch, and transmission 3rd gear apply switch. The ECM will engage TCC by grounding circuit No. 422 to energize solenoid.

TCC will engage when vehicle speed is greater than 30 MPH, engine at normal operating temperature (greater than 158°F/70°C), throttle position sensor output not changing (indicating a steady road speed), transmission 3rd gear switch closed, and brake switch closed.

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

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 by grounding circuit No. 422. This test checks capability of ECM to control solenoid.

A thermostat that is stuck in the open position, or opens at too low a temperature, may result in an inoperative TCC.

Note. ECM terminal B7 on early L Body is F6.

Note. DO NOT perform this test without supporting the lower control arms so that the drive axles are in a normal horizontal position. Running the vehicle in gear with the wheels hanging down at full travel may damage the drive axles.

Chart C-8, Torque Converter Clutch 2.0L (VIN 1) TBI - J & L Bodies. Scheme 119

CODE 24, VEHICLE SPEED SENSOR 2.0L (VIN 1) TBI - J BODY

Vehicle speed information is provided to the ECM on circuit No. 437 by the vehicle speed sensor, which is mounted in instrument panel. ECM supplies 12 volts on this circuit. VSS alternately grounds and opens circuit No. 437 when drive wheels are turning. This pulsing action will occur about 2000 times per mile. ECM then converts the pulsing action to MPH.

The VSS buffer supplies the necessary signal for the instrument panel for operating the speedometer and the odometer. If the vehicle is equipped with cruise control, the VSS also provides a signal to the cruise control module.

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

1. Code 24 will set if vehicle speed equals zero mph when the following conditions occur: Engine speed is between 1200 and 4400 RPM. Low load condition, low MAP voltage, high manifold vacuum. Not in Park or Neutral. All conditions met for 5 seconds. These conditions are met during a road load deceleration. Disregard Code 24 that sets when drive wheels are not turning.
2. 8-12 volts at the I. P. connector indicates circuit No. 437 is open between the I. P. connector and VSS, or VSS is faulty. Voltage of less than one volt at I. P. connector indicates circuit No. 437 is shorted to ground. If voltage reads greater than 10 volts after disconnecting circuit No 437 at VSS, VSS is faulty. If voltage remains less than 8 volts, check for grounded circuit No. 437 wire. If wire is not grounded, ECM or ECM connector is faulty.

The "Scan" tester should indicate a vehicle speed whenever the drive wheels are turning more than 3 mph. On vehicles with automatic transmissions, a faulty or misadjusted Park or Neutral safety switch can result in a false Code 24. Use the "Scan" tester to check for proper signal (same indicated speed) while in drive.

Code 24: Vehicle Speed Sensor Flow Chart (J Body). Scheme 120

Note. DO NOT perform this test without supporting the lower control arms so that the drive axles are in a normal horizontal position. Running the vehicle in gear with the wheels hanging down at full travel may damage the drive axles.

Code 24, Vehicle Speed Sensor 2.0L (VIN 1) TBI - J Body. Scheme 121

Code 24: Vehicle Speed Sensor Ckt Diag. (J Body). Scheme 122

CODE 24, VEHICLE SPEED SENSOR 2.0L (VIN 1) TBI - L BODY

Vehicle speed information is provided to the ECM by the vehicle speed sensor, which is a Permanent Magnet (PM) generator. It is mounted in the transaxle. The PM generator produces a pulsing voltage whenever vehicle speed is over 3 MPH. The A/C voltage level and the number of pulses increases with vehicle speed. The ECM then converts the pulsing voltage to MPH, which is used for calculations. MPH can be displayed with the "Scan" tester and should match speedometer reading.

The function of VSS buffer used in past model years has been incorporated into the ECM. The ECM then supplies the necessary signal for the instrument panel (4000 pulses per mile) for operating the speedometer and the odometer. If the vehicle is equipped with cruise control, the ECM also provides a signal (2000 pulses per mile) to the cruise control module.

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

Code 24 will set if vehicle speed equals 20 MPH when the following conditions occur

1. Engine speed is between 1100 and 4400 RPM.
2. Low load condition, low MAP voltage, high manifold vacuum.
3. Not in Park or Neutral.
4. All conditions met for 5 seconds.

These conditions are met during a road load deceleration. Disregard Code 24 that sets when drive wheels are not turning. The PM generator only produces a signal when the drive wheels are turning more than 3 MPH.

The "Scan" tester should indicate a vehicle speed whenever the drive wheels are turning more than 3 MPH. A problem in circuit No. 938 will not affect the VSS input or the reading on the "Scan" tester. Check circuits No. 400 and 401 for proper connections. Make sure connections are clean and tight and the harness is routed correctly.

On vehicles with automatic transmissions, a faulty or misadjusted Park or Neutral safety switch can result in a false Code 24. Use the "Scan" tester and check for proper signal while in Drive. "Scan" reading should match speedometer.

Code 24: Vehicle Speed Sensor Flow Chart (L Body). Scheme 123

Note. DO NOT perform this test without supporting the lower control arms so that the drive axles are in a normal horizontal position. Running the vehicle in gear with the wheels hanging down at full travel may damage the drive axles.

Code 24, Vehicle Speed Sensor 2.0L (VIN 1) TBI - L Body. Scheme 124

Code 24: Vehicle Speed Sensor Ckt Diag. (L Body). Scheme 125

CHART C-1A, PARK/NEUTRAL SWITCH 2.0L (VIN 1) TBI - J & L BODIES

The Park/Neutral switch contacts are part of neutral start switch. They 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 volt. The ECM uses this signal as one of the inputs to control IAC and VSS diagnostics.

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

1. Checks for a closed switch to ground with transmission in Park position. Different makes of "Scan" testers will display P/N status differently. Refer to manufacturer's tester operation manual for type of display used.
2. Checks for an open switch circuit in Drive.
3. Be sure "Scan" indicates Drive, even while wiggling shifter to test for an intermittent or misadjusted switch in Drive.

Chart C-1A: Park/Neutral Switch (A/T) Flow Chart. Scheme 126

Chart C-1A, Park/Neutral Switch 2.0L (VIN 1) TBI - J & L Bodies. Scheme 127

CHART C-8, TORQUE CONVERTER CLUTCH 4.3L & 5.0L (VIN E) TBI B, F & G BODIES (1 OF 2)

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

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

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

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

Flow Chart C8A, 200-4R TCC Electrical Diagnosis. Scheme 128

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

1. Coolant Temperature Should Be Above 65°C
2. TPS - Be Sure TPS Signal Is Not Erratic
3. VSS - Be Sure "Scan" Displays VSS With Drive Wheels Turning

If Code 24 Is Present, See Code Chart 24

Chart C-8, Torque Converter Clutch 4.3L & 5.0L (VIN E) TBI B, F & G Bodies (1 OF 2). Scheme 129

CHART C-8, TORQUE CONVERTER CLUTCH 4.3L & 5.0L (VIN E) TBI B, F & G BODIES (2 OF 2)

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

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

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

Flow Chart C8A (2 of 2), TCC Electrical Diagnosis. Scheme 130

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

Chart C-8, Torque Converter Clutch 4.3L & 5.0L (VIN E) TBI B, F & G Bodies (2 OF 2). Scheme 131

CODE 24, VEHICLE SPEED SENSOR 4.3L TBI - B & G BODIES

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

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

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

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

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

Code 24 Schematic: Vehicle Speed Sensor ("B" & "G" Bodies). Scheme 132

Flow Chart, Code 24: Vehicle Speed Sensor ("B" & "G" Bodies). Scheme 133

Code 24, Vehicle Speed Sensor 4.3L TBI - B & G Bodies. Scheme 134

CODE 24, VEHICLE SPEED SENSOR 5.0L (VIN E) TBI - F BODY

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

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

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

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

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

Code 24 Schematic: Vehicle Speed Sensor ("F" Body). Scheme 135

Flow Chart, Code 24: Vehicle Speed Sensor ("F" Body). Scheme 136

Code 24, Vehicle Speed Sensor 5.0L (VIN E) TBI - F Body. Scheme 137

CHART C-1A, PARK/NEUTRAL SWITCH 4.3L & 5.0L (VIN E) TBI - B, F & G BODIES

The Park/Neutral switch contacts are a part of the neutral start switch. Contacts are closed to ground in Park or Neutral. The ECM applies and monitors a 12-volt signal on circuit No. 434 and senses a closed switch when voltage drops to less than one volt. If circuit No. 434 indicates Park/Neutral (grounded) while in Drive, the EGR system would be inoperative, resulting in possible detonation. If circuit No. 434 indicates Drive (open), a dip in idle may exist when gear selector is moved to Drive.

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

1. Checks for a switch closed to ground in Park.
2. Checks for an open switch in Drive.
3. To test for an intermittent or misadjusted switch in Drive, be sure "Scan" tester indicates Drive, even while wiggling shifter.

Flow Chart - Park/Neutral Switch ("F" Body). Scheme 138

Chart C-1A, Park/Neutral Switch 4.3L & 5.0L (VIN E) TBI - B, F & G Bodies. Scheme 139

CHART C-8, TORQUE CONVERTER CLUTCH 2.0L PFI - J & N BODIES

The purpose of the automatic transmission/transaxle Torque Converter Clutch (TCC) feature is to eliminate power loss of torque converter stage when vehicle is in a 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 a brake switch, and transmission 3rd gear apply switch. The ECM will engage TCC by grounding circuit No. 422 to energize solenoid.

TCC will engage when vehicle speed is greater than 30 MPH, engine at normal operating temperature (greater than 158°F/70°C), throttle position sensor output not changing (indicating a steady road speed), transmission 3rd gear switch closed, and brake switch closed.

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

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 by grounding circuit No. 422. This test checks capability of ECM to control solenoid.

A thermostat that is stuck in the open position, or opens at too low a temperature, may result in an inoperative TCC.

Note. ECM terminal B7 on early L Body is F6.

Note. DO NOT perform this test without supporting the lower control arms so that the drive axles are in a normal horizontal position. Running the vehicle in gear with the wheels hanging down at full travel may damage the drive axles.

Chart C-8, Torque Converter Clutch 2.0L PFI - J & N Bodies. Scheme 140

CODE 24, VEHICLE SPEED SENSOR 2.0L PFI - J & N BODIES

Vehicle speed information is provided to the ECM by the vehicle speed sensor, which is a Permanent Magnet (PM) generator. It is mounted in the transaxle. The PM generator produces a pulsing voltage whenever vehicle speed is over 3 MPH. The A/C voltage level and the number of pulses increases with vehicle speed. The ECM then converts the pulsing voltage to MPH, which is used for calculations. MPH can be displayed with the "Scan" tester and should match speedometer reading.

The function of VSS buffer used in past model years has been incorporated into the ECM. The ECM then supplies the necessary signal for the instrument panel (4000 pulses per mile) for operating the speedometer and the odometer. If the vehicle is equipped with cruise control, the ECM also provides a signal (2000 pulses per mile) to the cruise control module.

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

Code 24 will set if vehicle speed equals 20 MPH when the following conditions occur

1. Engine speed is between 1100 and 4400 RPM.
2. Low load condition, low MAP voltage, high manifold vacuum.
3. Not in Park or Neutral.
4. All conditions met for 5 seconds.

These conditions are met during a road load deceleration. Disregard Code 24 that sets when drive wheels are not turning. The PM generator only produces a signal when the drive wheels are turning more than 3 MPH.

The "Scan" tester should indicate a vehicle speed whenever the drive wheels are turning more than 3 MPH. A problem in circuit No. 938 will not affect the VSS input or the reading on the "Scan" tester. Check circuits No. 400 and 401 for proper connections. Make sure connections are clean and tight and the harness is routed correctly.

On vehicles with automatic transmissions, a faulty or misadjusted Park or Neutral safety switch can result in a false Code 24. Use the "Scan" tester and check for proper signal while in Drive. "Scan" reading should match speedometer.

Note. DO NOT perform this test without supporting the lower control arms so that the drive axles are in a normal horizontal position. Running the vehicle in gear with the wheels hanging down at full travel may damage the drive axles.

Code 24, Vehicle Speed Sensor 2.0L PFI - J & N Bodies. Scheme 141

CHART C-1A, PARK/NEUTRAL SWITCH 2.0L PFI - J & N BODIES

The Park/Neutral switch contacts are part of neutral start switch. They 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 volt. The ECM uses this signal as one of the inputs to control IAC and VSS diagnostics.

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

1. Checks for a closed switch to ground with transmission in Park position. Different makes of "Scan" testers will display P/N status differently. Refer to manufacturer's tester operation manual for type of display used.
2. Checks for an open switch circuit in Drive.
3. Be sure "Scan" indicates Drive, even while wiggling shifter to test for an intermittent or misadjusted switch in Drive.

Chart C-1A, Park/Neutral Switch 2.0L PFI - J & N Bodies. Scheme 142

CHART C-8, TORQUE CONVERTER CLUTCH 2.3L PFI - N BODY

The purpose of the TCC is to prevent converter slippage during cruise conditions. Once the TCC is engaged, all slippage is eliminated, improving fuel economy. Fused battery voltage is supplied to the TCC solenoid through the brake switch, and transmission 3rd gear apply switch. ECM will engage TCC by grounding circuit No. 422 to energize solenoid. The TCC will engage under the following conditions

1. Vehicle road speed exceeds calibrated value of about 34 MPH (55km/h).
2. TPS not varying signal, indicating a steady road speed.
3. Transmission 2nd gear switch closed.
4. Brake switch closed. NOTE: Test numbers refer to test numbers on diagnostic chart. If light is not illuminated, this confirms transmission 2nd gear apply switch is open. Transmission 2nd gear apply switch should close at 25 MPH. Test light should illuminate and confirm battery voltage, and closed brake switch. Grounding diagnostic terminal with ignition on and engine off, should energize TCC solenoid. When terminal is grounded, circuit No.422 is simultaneously grounded. This test ECM's ability to supply a ground to the TCC solenoid. Test light should illuminate when connected to battery voltage and ALDL terminal "F". This illumination occurs as circuit No. 422 is grounded.

"Scan" tester will only indicate whether ECM has turned on TCC driver, and does not confirm that TCC has engaged. Check for RPM drop as "Scan" tester indicates TCC driver has been turned on. If RPM drops occurs, TCC has engaged.

Chart C8A Schematic - TCC Electrical Diagnosis (N Body). Scheme 143

Flow Chart C8A - TCC Electrical Diagnosis (N Body). Scheme 144

Note. DO NOT perform this test without supporting the lower control arms so that the drive axles are in a normal horizontal position. Running the vehicle in gear with the wheels hanging down at full travel may damage the drive axles.

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

1. TPS - Be Sure TPS Signal Is Not Erratic.
2. VSS - Should Indicate VSS With Wheels Turning.
3. Codes - If 24 Is Present, See Code 24 Chart.

Chart C-8, Torque Converter Clutch 2.3L PFI - N Body. Scheme 145

CODE 24, VEHICLE SPEED SENSOR 2.3L PFI - N BODY

The speed sensor, a Permanent Magnet (PM) generator, provides ECM with vehicle speed information. The PM generator, mounted in the transmission, produces a pulsing voltage signal whenever vehicle speed is greater than 3 MPH. The AC voltage level and the number of pulses increase with vehicle speed. ECM converts pulsing voltage to MPH, which is used for calculations. MPH can be displayed with a scan tool. Output of generator can be monitored with a digital voltmeter on the AC scale while rotating generator.

The function of the VSS buffer used in past models years has been incorporated into the ECM. The ECM supplies the signal for the instrument panel (4000 pulses per mile) to operate the speedometer, and for the odometer and cruise control (2000 pulses per mile).

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

1. Code 24 will set only when following conditions are met: Engine RPM is between 1600 and 3600. TPS is less than 7 percent. Gear selector not in park or neutral. All conditions met for 20 seconds. No Codes 21 or 22. The above conditions are met during road load deceleration. Ignore a Code 24 that is set when the drive wheels are turning faster than 3 MPH.
2. Ensure that correct PROM is used before replacing ECM.

Vehicle speed should be indicated whenever drive wheels are rotating greater than 3 MPH. Ensure that circuits No. 400 and 401 have proper connections. Also check for correct harness routing.

Note. On vehicles with automatic transmission, a faulty or improperly adjusted park/neutral switch can result in a false Code 24. Use a scan tool and check for proper signal while in drive. Refer to CHART C1A for P/N switch diagnosis check.

Code 24 Schematic - VSS Circuit (N Body). Scheme 146

Code 24 Flow Chart - VSS Circuit (N Body). Scheme 147

Note. DO NOT perform this test without supporting the lower control arms so that the drive axles are in a normal horizontal position. Running the vehicle in gear with the wheels hanging down at full travel may damage the drive axles. Disregard Code 24 if set while drive wheels are not turning.

Code 24, Vehicle Speed Sensor 2.3L PFI - N Body. Scheme 148

CHART C-1A, PARK/NEUTRAL SWITCH 2.3L PFI - N BODY

The Park/Neutral switch contacts are a part of the neutral start switch and 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 volt. The ECM uses the P/N signal as one of the inputs to control Idle Air Control (IAC) and VSS diagnostics.

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

1. This test checks for a closed switch to ground in Park position. If using an ohmmeter, instead of a test light or "Scan" tester, the resistance will be low, indicating continuity to ground.
2. This test checks for an open switch in Drive range.
3. Ensure that "Scan" tester indicates Drive while wiggling shifter to test for a faulty or misadjusted switch.

Chart C1A Schematic - Park/Neutral Switch (N Body). Scheme 149

Flow Chart C1A - Park/Neutral Switch (N Body). Scheme 150

Chart C-1A, Park/Neutral Switch 2.3L PFI - N Body. Scheme 151

CHART C-8, TORQUE CONVERTER CLUTCH 2.8L PFI - A, J, L & P BODIES

The purpose of the Torque Converter Clutch (TCC) feature is to eliminate the power loss of the transmission converter stage when the vehicle is in a cruise condition. This allows the convenience of the automatic transmission and the fuel economy of a manual transmission. Electrical power from the ignition circuit is supplied to the TCC solenoid through the brake switch and transmission 3rd gear switch. The ECM will engage TCC by grounding circuit No. 422 to energize the solenoid.

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

1. If test light is off, this confirms 3rd gear switch is open.
2. At 25 MPH, the 3rd gear switch should close. Test light will come on and confirm battery supply and closed brake switch.
3. Grounding the diagnostic "test" terminal with ignition on and engine off should energize the TCC solenoid when ECM grounds circuit No. 422. This test checks the ability of the ECM to supply a ground to the TCC solenoid. The test light connected from 12 volts to ALDL terminal "F" will turn on as circuit No. 422 is grounded.

The "Scan" tester only indicates when the ECM has turned on the TCC driver. This does not confirm that the TCC has engaged. To determine if TCC is functioning properly, note engine RPM. RPM should decrease when "Scan" tester indicates TCC driver has turned on.

Chart C8A Schematic, Torque Converter Clutch (A/J/L Bodies). Scheme 152

Chart C8A Schematic, Torque Converter Clutch (P Bodies). Scheme 153

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

1. Coolant Temperature Should Be Above 65°.
2. TPS - Be Sure TPS Signal Is Not Erratic.
3. VSS - Should Indicate VSS With Wheels Turning.
4. Codes - If 24 Is Present, See Code Chart 24.

Chart C-8, Torque Converter Clutch 2.8L PFI - A, J, L & P Bodies. Scheme 154

CHART C-8, TORQUE CONVERTER CLUTCH 2.8L PFI A & W BODIES WITH 440-T4 (1 OF 2)

The Torque Converter Clutch (TCC) feature eliminates power loss of the torque converter when the vehicle is in a cruise mode. This allows the convenience of an automatic and the fuel economy of a manual transmission. The heart of the system is a solenoid located inside the transmission, which is controlled by the ECM.

When the solenoid coil is activated, the torque converter clutch is applied, which results in straight through mechanical coupling from the engine to the wheels. When the transmission solenoid is deactivated, the TCC is released, which allows the torque converter to operate in the conventional manner (fluidic coupling between engine and transmission).

The TCC will engage when the following conditions occur

1. Engine is warmed up.
2. Vehicle speed is greater than a calibrated value.
3. Throttle position sensor output is not changing, indicating a steady road speed.
4. Brake switch is closed. NOTE: Test numbers refer to test numbers on diagnostic chart. This test checks the continuity of the TCC circuit from the fuse to the ALDL connector. When the brake pedal is released, the light should come back on and then go off when the diagnostic "test" terminal is grounded. This will test circuit No. 422 and the TCC drive in the ECM.

The "Scan" tester only indicates when the ECM has turned on the TCC driver. This does not confirm that the TCC has engaged. To determine if the TCC is functioning properly, observe engine RPM. The RPM should decrease when the "Scan" tester indicates the TCC driver has turned on.

Chart C-8B Schematic, Torque Converter Clutch (A Body). Scheme 155

Chart C-8B, Torque Converter Clutch (A Body). Scheme 156

Chart C-8B, Torque Converter Clutch (W Body) (1 of 2). Scheme 157

CHART C-8, TORQUE CONVERTER CLUTCH 2.8L PFI A & W BODIES WITH 440-T4 (2 OF 2)

The 3rd gear switch is open both in 3rd and 4th gear. The 4th gear switch is open only in 4th gear, which allows for TCC when in 4th gear. The TCC will disengage during a 4-3 downshift.

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

1. Some "Scan" testers display the status of these switches in different ways. Be familiar with the type of tester being used. Since both switches should be in the closed state during this test, the tester should read the same for either the 3rd or 4th gear switch.
2. Determines whether the switch or signal circuit is open. The circuit can be checked for an open by measuring the voltage (with a voltmeter) at the TCC connector. Reading should be about 12 volts.
3. Because the switch should be grounded in this step, disconnecting the TCC connector should cause the "Scan" tester status to change.
4. The switch status should change when the vehicle shifts into 3rd gear.

If vehicle is road tested because of a TCC related problem, be sure the switch status does not change while in 4th gear because the TCC will disengage. If switches change state, carefully check wire routing and connections.

Chart C-8B, Torque Converter Clutch Schematic. Scheme 158

Chart C-8B, Torque Converter Clutch (A & W Body) (2 of 2). Scheme 159

CHART C-8, TORQUE CONVERTER CLUTCH 2.8L, 5.0L & 5.7L PFI - F BODY (1 OF 2)

The purpose of the Torque Converter Clutch (TCC) feature is to eliminate the power loss of the torque converter stage when the vehicle is in a cruise condition. This allows the convenience of the automatic transmission and the fuel economy of a manual transmission. The heart of the system is a solenoid located inside the automatic transmission which is controlled by the ECM.

When the solenoid coil is activated, the TCC is applied through a mechanical coupling from the engine to transmission. When the transmission solenoid is de-energize, the TCC is released which allows the torque converter to operate in the conventional manner (fluidic coupling between engine and transmission). The ECM turns on the TCC when coolant temperature is greater than 149°F (65°C), TPS is not changing and vehicle speed is greater than a specified value.

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

1. When a test light is connected from ALDL terminal "F" to ground, a test light on indicates battery voltage is okay and the TCC solenoid is disengaged.
2. When the diagnostic "test" terminal is grounded, the ECM should energize the TCC solenoid and the test light should go out.

A "Scan" tester only indicates when the ECM has turned on the TCC driver (grounded circuit No. 422). This does not confirm that the TCC has engaged. To determine if TCC is functioning properly, observe engine RPM. RPM should decrease when the "Scan" tester indicates the TCC driver has turned on. The switches will not prevent TCC from functioning, but will affect TCC lock and unlock points. If the 4th gear switch circuit is always open the TCC may engage as soon as sufficient oil pressure is reached.

Torque Converter Clutch (5.0L/5.7L F Body). Scheme 160

Chart C-8, Torque Converter Clutch 2.8L, 5.0L & 5.7L PFI - F Body (1 Of 2). Scheme 161

CHART C-8, TORQUE CONVERTER CLUTCH 2.8L, 5.0L & 5.7L PFI - F BODY (2 OF 2)

A 4th gear switch (mounted in the transmission) opens when the transmission shifts into 4th gear. This switch is used by the ECM to modify TCC lock and unlock points (when in a 4-3 downshift).

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

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

A road test may be necessary to verify the problem. If the "Scan" tester indicates TCC is turning on and off erratically, check the status of the 4th gear switch to be sure it is not changing under a steady throttle position. If the switch is changing, check connections and wire routing carefully. If the 4th gear switch is always open the TCC may engage as soon as sufficient oil pressure is reached.

Torque Converter Clutch (5.0L/5.7L F Body). Scheme 162

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

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

Chart C-8, Torque Converter Clutch 2.8L, 5.0L & 5.7L PFI - F Body (2 Of 2). Scheme 163

CHART C-8, TORQUE CONVERTER CLUTCH 5.7L PFI - Y BODY (1 OF 2)

The purpose of the Torque Converter Clutch (TCC) feature is to eliminate the power loss of the torque converter stage when the vehicle is in a cruise condition. This allows the convenience of the automatic transmission and the fuel economy of a manual transmission. The heart of the system is an ECM controlled solenoid located inside the automatic transmission.

When the solenoid coil is activated, the TCC is applied through a mechanical coupling from the engine to transmission. When the transmission solenoid is de-energized, the TCC is released, allowing the torque converter to operate in the conventional manner (fluidic coupling between engine and transmission). The ECM turns on the TCC when coolant temperature is greater than 149°F (65°C), TPS is not changing and vehicle speed is greater than a specified value.

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

1. When a test light is connected from ALDL terminal "F" to ground, a test light on indicates battery voltage is okay and the TCC solenoid is disengaged.
2. When the diagnostic "test" terminal is grounded, the ECM should energize the TCC solenoid and the test light should go out.

A "Scan" tester only indicates when the ECM has turned on the TCC driver (grounded circuit No. 422). This does not confirm that the TCC has engaged. To determine if TCC is functioning properly, observe engine RPM. RPM should decrease when the "Scan" tester indicates the TCC driver has turned on. The switches will not prevent TCC from functioning, but will affect TCC lock and unlock points.

Torque Converter Clutch (5.7L Y Body). Scheme 164

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

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

Chart C-8, Torque Converter Clutch 5.7L PFI - Y Body (1 Of 2). Scheme 165

CHART C-8, TORQUE CONVERTER CLUTCH 5.7L PFI - Y BODY (2 OF 2)

The overdrive switch (mounted in the console) is used to modify TCC engagement speeds. The TCC will engage on a warm engine, under a given road load, in 2nd, 3rd and 4th gear, at about 30 MPH, if the gear selector is in Overdrive. If 2nd or Drive is selected, the overdrive switch should be closed and the ECM will not engage TCC until vehicle speed reaches about 40 MPH. This switch will help eliminate the TCC from engaging and disengaging while in city traffic. A 4th gear switch (mounted in the transmission) opens when the transmission shifts into 4th gear. This switch is used by the ECM to modify TCC lock and unlock points when in a 4-3 downshift maneuver.

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

1. With the gearshift in Overdrive, the "Scan" tester should display "YES". In this position the TCC will engage at about 30 MPH.
2. Circuit No. 925 can be checked for continuity by measuring for the 12-volt signal from the ECM with a DVOM. If the 12-volt signal is present, the switch is misadjusted or faulty.
3. This step should cause the switch to close and "Scan" tester should display "NO".
4. Unless the switch or circuit No. 446 is open, the "Scan" tester should display "NO", indicating the transmission is not in 4th gear. The 4th gear switch should only be open while in 4th gear.
5. This step determines if the ECM and wiring are okay. Grounding circuit No. 446 should cause the "Scan" tester to display "NO", indicating the transmission is not in 4th gear.
6. This step checks the operation of the 4th gear switch. When the transmission shifts into 4th gear, the switch should open and the tester should display "YES".
7. Disconnecting the TCC connector simulates an open switch. This determines if circuit No. 446 is shorted to ground or the problem is in the transmission.

A road test may be needed to verify customer complaint. If the "Scan" tester indicates TCC is turning on and off erratically, check the status of the 4th gear switch and the overdrive switch to be sure they are not changing during steady throttle. If the switches are changing status, check connections and wire routing carefully.

Torque Converter Clutch (5.7L Y Body). Scheme 166

Chart C-8, Torque Converter Clutch 5.7L PFI - Y Body (2 Of 2). Scheme 167

CODE 24, VEHICLE SPEED SENSOR 2.8L, 5.0L & 5.7L PFI A, F, J, P & Y BODIES

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

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

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

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

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

Code 24 Schematic, Vehicle Speed Sensor (A Body). Scheme 168

Code 24 Schematic, Vehicle Speed Sensor (J Body). Scheme 169

Code 24 Schematic, Vehicle Speed Sensor (F & P Bodies). Scheme 170

Code 24 Schematic, Vehicle Speed Sensor (5.0L & 5.7L F & Y Bodies). Scheme 171

Code 24, Vehicle Speed Sensor 2.8L, 5.0L & 5.7L PFI A, F, J, P & Y Bodies. Scheme 172

CODE 24, VEHICLE SPEED SENSOR 2.8L PFI - L & W BODIES

The ECM monitors the output from the Permanent Magnet (PM) generator mounted in the transaxle on circuits No. 400 and 401. The PM generator produces a pulsating, alternating current whenever vehicle speed is greater than 3 MPH. The AC voltage level and the number of pulses increases with vehicle speed. The ECM will calculate vehicle speed based on the time between pulses. The VSS buffer used on other models is incorporated into the ECM on these models.

If the vehicle is equipped with a digital speedometer and odometer and/or cruise control. The ECM provides pulses for operation of these components (2000 and 4000 pulses per mile respectively). The "Scan" tester reading should closely match speedometer reading when drive wheels are turning.

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

1. Code 24 will set if vehicle speed equals zero MPH when engine speed is between 1400 and 3600 RPM, throttle opening is less than 2 percent, a low load condition exists and transmission is not in Park or Neutral. All conditions must be met for 4-5 seconds during a road load deceleration. Disregard Code 24 that sets when drive wheels are not turning.

If "Scan" tester displays vehicle speed, check Park/Neutral switch operation using appropriate C-1 CHART. If switch is okay, check for intermittent connections.

Code 24 Flow Chart - Vehicle Speed Sensor (L Body). Scheme 173

Code 24 Flow Chart - Vehicle Speed Sensor (W Body). Scheme 174

Note. Disregard Code 24 If Set While Drive Wheels Are Not Turning

Code 24, Vehicle Speed Sensor 2.8L PFI - L & W Bodies. Scheme 175

CHART C-1A, PARK/NEUTRAL SWITCH 2.8L, 5.0L & 5.7L PFI A, F, J, L, P, W & Y BODIES

The Park/Neutral switch contacts are a part of the neutral start switch. Contacts are closed to ground in Park or Neutral. The ECM applies and monitors a 12-volt signal on circuit No. 434 and senses a closed switch when voltage drops to less than one volt. If circuit No. 434 indicates Park/Neutral (grounded) while in Drive, the EGR system would be inoperative, resulting in possible detonation. If circuit No. 434 indicates Drive (open), a dip in idle may exist when gear selector is moved to Drive.

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

1. Checks for a switch closed to ground in Park.
2. Checks for an open switch in Drive.
3. To test for an intermittent or misadjusted switch in Drive, be sure "Scan" tester indicates Drive, even while wiggling shifter.

Chart C1A Schematic, Park/Neutral Sw. (A & L Bodies). Scheme 176

Chart C1A Schematic, Park/Neutral Sw. (J Body). Scheme 177

Chart C1A Schematic, Park/Neutral Sw. (F & Y Bodies). Scheme 178

Chart C1A Schematic, Park/Neutral Sw. (P Body). Scheme 179

Chart C-1A, Park/Neutral Switch 2.8L, 5.0L & 5.7L PFI A, F, J, L, P, W & Y Bodies. Scheme 180

Flow Chart - Park/Neutral Switch (W Body). Scheme 181

CHART C-1, ECM QUAD-DRIVER CHECK 2.8L PFI - F & P BODIES

To energize controlled devices, the ECM uses integrated circuits called "Quad-Drivers" in place of separate transistors. Each Quad-Driver has 4 separate circuits that can be turned on or off independently. The ECM used on this vehicle (part No. 1227302) does not have fault protection, therefore, a single faulty circuit many times causes all 4 Quad-Driver circuits to fail. Because of increased current flow, 2 Quad-Drivers are used to drive the Torque Converter Clutch (TCC) solenoid. A faulty circuit is the largest cause of a failed Quad-Driver, therefore, this check should be performed whenever instructed to "Replace ECM" or whenever ECM exhibits characteristics of a damaged Quad-Driver, such as the following

1. SERVICE ENGINE SOON light on, with no stored codes.
2. Engine will not start and/or ECM will not flash Code 12.
3. Flickering, intermittent or dim SERVICE ENGINE SOON light.
4. Output, such as the TCC, is inoperative or constantly "on".
5. Engine misfires, surges or stalls.
6. Scan tester is erratic or inoperative.

ECM NO. 1227170 QUAD-DRIVER CIRCUIT IDENTIFICATION

ECM NO. 1227302 QUAD-DRIVER CIRCUIT IDENTIFICATION

Chart C1: ECM Quad-Driver Check Schematic (F & P Bodies). Scheme 182

Chart C1: ECM Quad-Driver Check Flow Chart (F & P Bodies). Scheme 183

Note. Use this check procedure only after other diagnostic charts have determined that there was an ECM failure.

Chart C-1, ECM Quad-Driver Check 2.8L PFI - F & P Bodies. Scheme 184

CHART C-8, TORQUE CONVERTER CLUTCH 3.0L PFI - N BODY

The purpose of the Torque Converter Clutch (TCC) feature is to eliminate power loss when the vehicle is in a cruise condition. This allows the convenience of an automatic transmission and the fuel economy of a manual transmission.

Fused battery ignition is supplied to the TCC solenoid through the brake and 3rd gear switch. The ECM will engage TCC by grounding circuit No. 422 to energize the solenoid.

The TCC will engage when the following conditions occur

1. Engine warmed up to greater than 156°F (70°C).
2. Vehicle speed greater than about 45 MPH.
3. Throttle sensor output not changing, indicating a steady road speed.
4. 3rd gear switch closed.
5. Brake switch closed.

An engine coolant thermostat that is stuck open, or opens at too low a temperature, may result in an inoperative TCC.

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

1. When test light is off, this confirms 3rd gear switch is open.
2. At 30 MPH the 3rd gear switch should close. Test light will come on and confirm battery supply and closed brake switch.
3. Grounding the diagnostic terminal with ignition on and engine off, should energize the TCC solenoid by grounding circuit No. 422. This test checks the capability of the ECM to supply a ground for the TCC solenoid.
4. Solenoids and relays are turned on or off by ECM internal electronic switches called "drivers". Each driver is part of a group of 4 called "quad-drivers". Failure of one can damage any other driver in the set. Before replacing ECM, be sure to check the coil resistance of all solenoids and relays controlled by the ECM. When checking TCC solenoid, be sure to raise drive wheels (support drive axles) and run about 30 MPH to close 3rd gear switch.

Chart C8, Schematic (3.0L N Body). Scheme 185

Flow Chart C8, Torque Converter Clutch (3.0L N Body). Scheme 186

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

1. Coolant Temperature.
2. TPS.
3. VSS.
4. Codes - If 24 Is Present, See Code Chart 24 Also Perform Mechanical Checks, Such As Linkage, Oil Level, Etc., Before Using This Chart

Chart C-8, Torque Converter Clutch 3.0L PFI - N Body. Scheme 187

CHART C-8, TORQUE CONVERTER CLUTCH 3.8L PFI - A, C & H BODIES (1 OF 2)

The purpose of the Torque Converter Clutch (TCC) feature is to eliminate the power loss of the torque converter when the vehicle is in a cruise condition. This allows the convenience of an automatic and the fuel economy of a manual transaxle. The heart of the system is an ECM-controlled solenoid located inside the transaxle.

When the solenoid coil is energized, the torque converter clutch is applied, which results in straight through mechanical coupling from the engine to the wheels. When the transmission solenoid is deactivated, the torque converter clutch is released which allows the torque converter to operate in the conventional manner (fluidic coupling between engine and transmission). The TCC will engage when the following conditions occur

1. Engine warmed up.
2. Vehicle speed greater than 28 MPH.
3. Throttle position sensor output not changing, indicating a steady road speed.
4. Brake switch closed. NOTE: Test numbers refer to test numbers on diagnostic charts. This test checks the continuity of the TCC circuit from the fuse to the ALDL connector. When the brake pedal is released and the diagnostic terminal is grounded, the light should come back on and then go off. This tests circuit No. 422 and the TCC driver in the ECM.

The "Scan" tester only indicates when the ECM has turned on the TCC driver. This does not confirm that the TCC has engaged. To determine if TCC is functioning properly, monitor engine RPM. Engine RPM should decrease when the "Scan" tester indicates the TCC driver has turned on.

Chart C8A, Schematic (3.8L A, C & H Bodies, 1 of 2). Scheme 188

Flow Chart C8A, TCC (3.8L A, C & H Bodies, 1 of 2). Scheme 189

Using A Scan Tool Check The Following And Correct As Necessary

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

Chart C-8, Torque Converter Clutch 3.8L PFI - A, C & H Bodies (1 Of 2). Scheme 190

CHART C-8, TORQUE CONVERTER CLUTCH 3.8L PFI - A, C & H BODIES (2 OF 2)

The 3rd gear switch in this vehicle is open in 3rd and 4th gear. The 4th gear switch is open in 4th gear, which allows for TCC when in 4th gear.

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

1. Some "Scan" testers display the state of these switches in different ways. Be familiar with the type of tester being used. Since both switches should be in the closed state during this test, the tester should read the same for either the 3rd or 4th gear switch.
2. Determines whether the switch or signal circuit is open. The circuit can be checked for an open by measuring the voltage (with a voltmeter) at the TCC connector. Voltage should be about 12 volts.
3. Because the switch should be grounded in this test, disconnecting the TCC connector should cause the "Scan" tester switch state to change.
4. The switch state should change when the vehicle shifts into 3rd gear.

If vehicle is road tested because of a TCC related problem, be sure the switch states do not change while in 4th gear, because the TCC will disengage. If switches change state, carefully check wire routing and connections.

Flow Chart C8B, TCC (3.8L A, C & H Bodies, 2 of 2). Scheme 191

Chart C-8, Torque Converter Clutch 3.8L PFI - A, C & H Bodies (2 Of 2). Scheme 192

CHART C-8, TORQUE CONVERTER CLUTCH 3.8L PFI (TURBO) - G BODY

The purpose of the converter clutch feature is to eliminate the power loss of the torque converter when the vehicle is in a cruise condition. This allows the convenience of an automatic and the fuel economy of a manual transmission. The heart of the system is an ECM-controlled solenoid which is located inside the transmission.

When the solenoid coil is energized, the torque converter clutch is applied, which results in straight through mechanical coupling from the engine to the wheels. When the transmission solenoid is deactivated, the torque converter clutch is released which allows the torque converter to operate in the conventional manner (fluidic coupling between engine and transmission). The TCC will engage on a warm engine under road load, in 4th gear only.

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

1. A test light on indicates battery voltage and continuity through TCC solenoid is okay.
2. Vacuum hose on throttle shaft pin increases TPS signal so TCC will engage without excessive wheel speed. Without the hose, it would require vehicle speed in excess of 65 MPH to engage TCC.
3. Checks for vehicle speed signal to ECM. Voltage should vary from 2-9 volts.
4. Checks 3rd and 4th gear signal to ECM. Signals will not prevent TCC engagement, but could cause a change in engagement and disengagement speed points.
5. Solenoids and relays are turned on or off by ECM internal electronic switches called "drivers". Each driver is part of a group of 4 called "quad-drivers". Failure of one can damage any other driver within the set.

Note. Before replacing ECM, be sure to check the coil resistance of all solenoids and relays controlled by the ECM.

Chart C8, Schematic (3.8L G Body). Scheme 193

Flow Chart C8, Torque Converter Clutch (3.8L G Body). Scheme 194

Chart C-8, Torque Converter Clutch 3.8L PFI (Turbo) - G Body (1 Of 2). Scheme 195

Chart C-8, Torque Converter Clutch 3.8L PFI (Turbo) - G Body (2 Of 2). Scheme 196

CODE 24, VEHICLE SPEED SENSOR 3.0L & 3.8L PFI - A, C, G & H BODIES

The Vehicle Speed Sensor (VSS) consists of a PM generator, buffer, speedometer and ECM. The PM generator is a permanent magnet assembly attached to the transmission or transaxle (in speedometer cluster on "A" body). As the vehicle moves, the generator creates a "sine wave" electrical pulse, which is routed to the buffer. In the buffer, the signal is changed from a "sine wave" to a "square wave" and amplified. The "square wave" is an on/off signal. The length of time between pulses determines vehicle speed. The ECM sends a 12-volt signal out on circuit No. 437. The frequency of the signal, which is pulsed low, is used by the ECM to determine vehicle speed.

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

1. Code 24 will set if vehicle speed equals zero MPH when the following conditions occur: Engine speed is between 1500 and 4000 RPM. TPS voltage reading shows closed throttle. Low load condition (low airflow). Not in Park or Neutral. All conditions met for 20 seconds.
2. Probe terminal "G" on "A" body. This test checks to see if the fault is circuit No. 437, including the ECM or the VSS/Buffer circuit. The ECM is the source of 12 volts via circuit No. 437 to the buffer in a normal working system.

Note. Disregard Code 24 that sets when the drive wheels are not turning.

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation.

Inspect ECM harness connector terminal "A10" for improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.

If connections and harness check out okay, raise drive wheels (support drive axles to prevent damage to CV joints). Block other wheels and idle engine more than 3 MPH, in low gear. Use "Scan" tester to check the vehicle speed while moving related connectors and wiring harness. If the failure is induced, the vehicle speed display will change. This may help to isolate the location of the malfunction. A shorted cruise control module or a faulty or misadjusted Park/Neutral switch can result in a false Code 24.

Code 24 Schematic (3.0L & 3.8L PFI - "A", "C", "G" & "H" Bodies). Scheme 197

Code 24 Flow Chart (3.0L & 3.8L PFI - "A", "C", "G" & "H" Bodies). Scheme 198

Code 24, Vehicle Speed Sensor 3.0L & 3.8L PFI - A, C, G & H Bodies. Scheme 199

CHART C-1A, PARK/NEUTRAL SWITCH 3.0L & 3.8L PFI - A, C, G & H BODIES

The Park/Neutral (P/N) switch contacts are a part of the neutral start switch and are closed to ground in Park or Neutral, and open in Drive. The ECM supplies ignition voltage through a current limiting resistor to circuit No. 434 and senses a closed switch when the voltage on circuit No. 434 drops to less than one volt. The ECM uses the P/N signal as one of the inputs to idle air control and VSS diagnostics.

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

1. This test checks for a closed switch to ground in Park position. Different makes of "Scan" tester will display P/N status differently. Refer to owners manual for display used.
2. This test checks for an open switch in Drive.
3. Be sure "Scan" tester indicates Drive, even while wiggling shifter. This will test for an intermittent condition due to an faulty or misadjusted P/N switch.

Chart C1A Schematic (3.0L & 3.8L PFI - "A", "C", "G" & "H" Bodies). Scheme 200

Chart C1A Flow Chart (3.0L & 3.8L PFI - "A", "C", "G" & "H" Bodies). Scheme 201

Chart C-1A, Park/Neutral Switch 3.0L & 3.8L PFI - A, C, G & H Bodies. Scheme 202

CHART C-8, TORQUE CONVERTER CLUTCH 3.8L "3800" PFI BONNEVILLE, ELECTRA & NINETY-EIGHT (1 OF 2)

The purpose of the torque converter clutch is to eliminate the power loss of the torque converter when vehicle is in cruise condition. This allows the convenience of automatic transmission and fuel economy of a manual transaxle. The heart of the system is a solenoid located inside the transaxle which is controlled by the ECM. When solenoid coil is activated (on), the torque converter clutch is applied which results in straight through mechanical coupling from engine to drive wheels. When the transaxle (TCC) solenoid is deactivated, the torque converter clutch is released which allows the torque converter to operate in the conventional manner (fluid coupling between engine and transaxle).

TCC will engage under the following conditions

1. Engine warmed to operating temperature.
2. Vehicle speed greater than a calibrated value (about 28 MPH).
3. TPS output not changing, indicating a steady road speed.
4. Brake switched closed. NOTE: Test numbers refer to test numbers on diagnostic charts. This test checks the continuity of TCC circuit from the fuse to ALDL connector. When brake pedal is released, light should come back on, and then go off when diagnostic terminal is grounded. This tests circuit No. 422 and TCC driver in ECM.

The "Scan" tester only indicates when ECM has turned on TCC driver, and this does not confirm that TCC has engaged. To determine if TCC is functioning properly, road test vehicle. Engine RPM should decrease when "Scan" tester indicates TCC driver has turned on.

Chart C8A (Bonneville, Electra & Ninety-Eight 1 of 2). Scheme 203

CHART C-8, TORQUE CONVERTER CLUTCH 3.8L "3800" PFI BONNEVILLE, ELECTRA & NINETY-EIGHT (2 OF 2)

Each gear switch opens when the appropriate clutch is applied. All gear switches are open in 4th gear.

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

1. Some "Scan" testers display the state of these switches in different ways. Read instructions on "Scan" tester usage before proceeding with test procedures. Since both switches should be in closed state during this test, "Scan" tester should indicate same readings for 2nd, 3rd or 4th gear switches.
2. Determines whether switch or signal circuit is open. The circuit can be checked for an open by measuring voltage at TCC connector. Reading should be about battery voltage. Because switch or switches should be grounded at some point in this procedure, unplugging TCC connector should cause "Scan" tester switch state to change. The switch state should change when vehicle shifts into 3rd gear.

If vehicle is road tested because of a TCC related problem, ensure switch states do not change while in 4th gear, because TCC will disengage. If switches change state, carefully check wire routing and connections.

Chart C8A (Bonneville, Electra & Ninety-Eight 2 of 2). Scheme 204

CODE 24, VEHICLE SPEED SENSOR 3.8L "3800" PFI BONNEVILLE, ELECTRA & NINETY-EIGHT

Vehicle speed information is provided to the ECM by the vehicle speed sensor, a permanent magnet (PM) generator mounted in the transmission. The PM generator produces a pulsing voltage whenever vehicle speed is greater than about 3 MPH. The AC voltage level and the number of pulses increases with vehicle speed. The ECM converts the pulsing voltage to MPH, and the MPH can be displayed with a "Scan" tester.

The function of the VSS buffer, used in their past model years, has been incorporated into the ECM. The ECM supplies the necessary signal for the instrument panel (4004 pulses per mile) for operating the speedometer and the odometer.

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

1. Code 24 will set if vehicle speed signal equals zero MPH when: Engine speed is between 1500 and 4000 RPM. TPS reading shows closed throttle. Low load condition (low air flow). Not in park or neutral. No Code 29 or 31. When vehicle is in 4th gear. All conditions met for 20 seconds. Disregard Code 24 that sets when drive wheels are not rotating. The PM generator only produces a signal if drive wheels are rotating faster than 3 MPH.
2. Before replacing the ECM, check MEM-CAL for correct application.

"Scan" tester should indicate a vehicle speed whenever drive wheels are rotating faster than 3 MPH. Check circuit No. 400 and 401 for proper connections. Ensure they are clean and tight, and harness is routed correctly. See INTERMITTENTS in TROUBLE SHOOTING section.

Code 24 Chart (Bonneville, Electra & Ninety-Eight). Scheme 205

CODE 31, PARK/NEUTRAL SWITCH 3.8L "3800" PFI BONNEVILLE, ELECTRA & NINETY-EIGHT

The Park/Neutral (P/N) switch contacts are part of the neutral start switch and are closed to ground in Park or Neutral, and open in Drive. The ECM supplies ignition voltage through a current limiting resistor to circuit No. 434 and senses a closed switch when the voltage on circuit No. 434 drops to less than one volt. The ECM uses the P/N signal as one of the inputs to idle air control, EGR and VSS diagnostics.

Code 31 will set under the following conditions

1. If circuit No. 434 indicates P/N (grounded) while in drive range and 4th gear TCC engaged, EGR would be inoperative, resulting in possible detonation.
2. If circuit No. 434 indicates drive (open) at start-up, a drop in idle may exist when gear selector is moved into drive range.
3. If transaxle 4th gear switch has an intermittent open, ECM thinks vehicle is in 4th gear and will set Code 31. NOTE: Test numbers refer to test numbers on diagnostic chart. Checks for a closed switch to ground in "PARK" position. Different types of "Scan" testers will read P/N differently. Refer to "Scan" tester operators manual for type of display used for specific tester. Checks for an open switch in drive range. Ensure "Scan" tester indicates Drive, even while wiggling shifter. This will test for an intermittent or misadjusted switch in Drive or Overdrive range.

Code 31 Chart (Bonneville, Electra & Ninety-Eight). Scheme 206

CHART C-8, TORQUE CONVERTER CLUTCH 3.8L "3800" PFI REATTA, RIVIERA & TORONADO

The purpose of the torque converter clutch is to eliminate the power loss of the torque converter when vehicle is in cruise condition. This allows the convenience of automatic transmission and fuel economy of a manual transaxle. The heart of the system is a solenoid located inside the transaxle which is controlled by the ECM.

When solenoid coil is activated (on), the torque converter clutch is applied which results in straight through mechanical coupling from engine to drive wheels. When the transaxle (TCC) solenoid is deactivated, the torque converter clutch is released which allows the torque converter to operate in the conventional manner (fluidic coupling between engine and transaxle).

TCC will engage under given road load in 3rd and 4th gear.

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

1. "LO" display confirms that 4th gear switch is closed.
2. At 45 MPH the transaxle 4th gear switch should open resulting in IPC displaying "HI".
3. Entering ECM diagnostics output data E001 should cause the solenoid to cycle on and off at 3 second intervals. This test checks the capability of the ECM to control the solenoid driver circuit.
4. Solenoids are turned on or off by the ECM internal electronic switches called "drivers". Each driver is part of a group of 4, called Quad-Drivers. Using an ohmmeter, check the solenoid coil resistance of the TCC. Coil resistance must measure greater than 20 ohms.

Chart C-8A (Reatta, Riviera & Toronado). Scheme 207

CODE EO24, VEHICLE SPEED SENSOR 3.8L "3800" PFI REATTA, RIVIERA & TORONADO

The VSS system incorporates 3 major components. They include the vehicle speed generator, the BCM, and the ECM. The vehicle speed generator is a permanent magnet assembly attached to the transaxle. As the vehicle moves, the generator creates a "sine wave" electrical pulse which is monitored by the BCM. In the BCM, this is amplified and "cleaned up" via the same process as used in a buffer. Part of this "cleaning up" involves changing the "sine wave" signal to a "square wave" signal or on/off type of signal. By determining the length of time between the "ON" and "OFF" portions of the signal, the BCM can interpret the vehicle speed. It then transmits this data via circuit No. 437 to the ECM.

Because of the circuitry involved, it is highly unlikely that a Code E024 alone will be caused by a faulty VSS. However, a combination of Codes E024 and B124 could represent this. In the case of a Code B124 accompanying a Code E024, see the appropriate charts in the BCM section first.

To set a Code E024, the following conditions must exist

1. Engine speed must be between 1500-4000 RPM.
2. LV8 reading (Diagnostics Data ED23) between 40 and 150 counts.
3. Vehicle speed less than 3 MPH.
4. Gear selector not in Park or Neutral.
5. Above conditions met for 40 seconds. NOTE: Test numbers refer to numbers on diagnostic chart. If a Code B124 is present also, refer to accompanying charts for diagnosis of B124 before attempting to diagnose E024. If ECM data display ED12 (vehicle speed) displays zero MPH, the ECM is not receiving a VSS input from the BCM. A zero MPH display at this point, indicates a fault which should have set a Code B124. Refer to that chart for the remainder of diagnosis. A display greater than zero, indicates a fault in circuit No. 437, faulty connections at the ECM or BCM, or a faulty ECM.

Code E024 Chart (Reatta, Riviera & Toronado). Scheme 208

CODE EO27, EO28, & EO29 2ND, 3RD & 4TH GEAR SWITCH 3.8L "3800" PFI REATTA, RIVIERA & TORONADO

Gear switches are located inside the transaxle. They are pressure operated switches, that are normally closed. The ECM supplies 12 volts through each selected circuit to switch. In any condition other than the specific gear application, signal line monitors low voltage or low potential. As road speed increases, hydraulic pressure is applied to specific gear clutches, and gear switch opens. During this time, ECM monitors high 12-volt potential and interprets this to indicate that gear is applied. The ECM uses gear signals to control fuel delivery (and TCC).

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

Code E027 will set under the following conditions

1. Circuit No. 581 indicates ground or closed switch when vehicle is in 4th gear operation.
2. Circuit No. 581 indicates an open (drive) when the engine is first started.

Code E028 will set under the following conditions

1. Circuit No. 108 indicates ground or closed switch when vehicle is in 4th gear operation.
2. Circuit No. 108 indicates an open (drive) when the engine is first started.

Code E029 will set under the following conditions

1. Circuit No. 446 indicates ground or closed switch when vehicle is in 4th gear operation.
2. Circuit No. 446 indicates an open (drive) when the engine is first started. Digital Volt/ohm Meter (DVM) must be used. A test light will not light due to the very low current being supplied by the ECM. Checks to see if circuit is grounded through switch. Checks for a good, properly operating switch. Also checks circuit within transaxle for an improper ground.

An intermittent may be caused by a poor connection, incorrectly routed harness, rubbed through wire insulation or a wire broken inside insulation. Check for the following

1. Poor Connection, at ECM pins. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal to wire connection.
2. Misrouted Harness. Inspect wiring harness to ensure that it is not too close to high voltage wires, such as spark plug leads.
3. Damaged Harness. Inspect harness for damage. If harness appears okay, "Scan" while moving related connectors and wiring harness. A change in display would indicate the intermittent fault location.

2nd, 3rd & 4th Gear Switch Diagnosis (Reatta, Riviera & Toronado). Scheme 209

CODE EO31, PARK/NEUTRAL SWITCH 3.8L "3800" PFI REATTA, RIVIERA & TORONADO

The Park/Neutral (P/N) switch contacts are part of the neutral start switch and are closed to ground in Park or Neutral, and open in Drive. The ECM supplies ignition voltage through a current limiting resistor to circuit No. 434 and senses a closed switch when the voltage on circuit No. 434 drops to less than one volt. The ECM uses the P/N signal as one of the inputs to idle air control, EGR and VSS diagnostics.

Code 31 will set under the following conditions

1. If circuit No. 434 indicates P/N (grounded) while in Drive range and 4th gear TCC engaged, EGR would be inoperative, resulting in possible detonation.
2. If circuit No. 434 indicates Drive (open) at start up, a drop in idle may exist when gear selector is moved into Drive range.
3. If transaxle 4th gear switch has an intermittent open, ECM thinks vehicle is in 4th gear and will set Code E031. NOTE: Test numbers refer to test numbers on diagnostic chart. Checks for a closed switch to ground in "PARK" position. Different types of "Scan" testers will read P/N differently. Refer to "Scan" tester operators manual for type of display used for specific tester. Checks for an open switch in drive range. Ensure that on-board diagnostics EI74 indicates drive ("HI"), even while wiggling shifter. This will test for an intermittent or misadjusted switch in drive or overdrive range.

Code E031 Chart (Reatta, Riviera & Toronado). Scheme 210

CODE EO38, BRAKE SWITCH 3.8L "3800" PFI REATTA, RIVIERA & TORONADO

The ECM monitors the status of brake switch circuits through ECM terminal "BC4". Code E038 will set under the following conditions

1. Code 24 is not present.
2. Vehicle speed has been greater than 35 MPH and back to zero MPH several times.
3. Status of circuit No. 420 has not changed state (high or low). NOTE: Test numbers refer to test numbers on diagnostic chart. This step checks for battery voltage available for circuit No. 420. Checks fuse, switch and circuit for battery voltage.

Code E038 Chart (Reatta, Riviera & Toronado). Scheme 211

CODE EO39, TORQUE CONVERTER CLUTCH 3.8L "3800" PFI REATTA, RIVIERA & TORONADO

The ECM controls TCC operation by grounding circuit No. 422 through the QDM. Code E039 will set under the following conditions

1. Code E029 is not present.
2. Brake switch is closed (off).
3. TCC is commanded by ECM.
4. Vehicle is in 4th gear.
5. The engine speed to vehicle speed ratio is outside of its window of operation.
6. All of the above for a time greater than 30 seconds. NOTE: Test numbers refer to numbers on diagnostic chart. Checks availability of battery voltage on circuit No. 420. Check fuse, brake switch and battery voltage circuit to the TCC solenoid.

Code E039 Chart (Reatta, Riviera & Toronado). Scheme 212

CODE B124, VEHICLE SPEED SENSOR 3.8L "3800" PFI REATTA, RIVIERA & TORONADO

The vehicle speed sensor uses a Permanent Magnet (PM) generator to generate an electrical signal representative of vehicle speed. This signal is brought to the BCM by circuit No. 400 (VSS high) and circuit No. 401 (VSS low), where the BCM buffers and amplifies the signal for its prospective uses. Output of the generator can be seen by using a digital voltmeter on the AC scale while rotating the generator drive (rotate front wheels).

Code B124 will set under the following conditions

1. Ignition on.
2. No Codes EO29, EO31 or B334.
3. Transaxle in 4th gear (EI82 "LOW")
4. No input to the BCM from the VSS.
5. Engine speed greater than 800 RPM.

During the time the failure is present, the continuous compressor at idle will be disabled, however, vehicle speed reading BD60 will display actual sensor reading.

Note. Test numbers refer to numbers on diagnostic chart.

1. Since the BCM amplifies and buffers the speed signal before it is sent to the ECM, Code EO24 in the ECM will set along with Code B124 in the BCM if the PM generator or circuits No. 400 and 401 have a problem. If Code B124 ever sets without setting a Code EO24, there is an internal problem in the BCM.
2. BCM data value BD60 displays MPH.
3. With the wheels turning, a voltage reading indicates that the PM generator and wiring are okay.
4. Checks for open in VSS circuit wiring.
5. Checks for ground in VSS circuit wiring prior to replacing sensor.

Note On Intermittents

If an intermittent Code B124 is being set, manipulate the related wiring while observing BCM data parameter BD60. If the failure is induced, the reading will jump from a normal value to zero MPH.

Code B124 Chart (Reatta, Riviera & Toronado). Scheme 213

CODE B127, GEAR SELECTOR SWITCH 3.8L "3800" PFI - TORONADO

The gear selector switch is mounted on the transaxle assembly. It is a multi-signal switch sending information relative to gear selector position to the BCM and ECM. The switch assembly also contains the neutral safety switch and back-up light switch, and provides park input to the automatic door lock module (if equipped). The switch uses 4 discrete circuits to pull 4 BCM terminal voltages low in various combinations to indicate each gear range. The voltage level of each of the circuits is represented in BCM data BD41. "0" = low, "1" = high. The 4 digits displayed represent decoder A, B, C and parity inputs in sequence.

The switch also provides park/neutral inputs to the ECM in a similar manner using one discrete input. This can be seen using ECM input EI74, where "HI" or "LO" represent the voltage level of input terminal. Code B127 will set if the following conditions occur

1. BCM gear selector switch input indicates P/N but ECM input does not.
2. BCM gear selector switch input does not indicate P/N but ECM input does.
3. Decoder and parity inputs do not agree with possible combinations.

If Code B127 is set, the DIC will display the warning message "GEAR SELECT PROBLEM" and IPC gear position display (PRND21) will flash.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks BCM inputs when only decoder A and parity circuit are pulled low.
2. Checks BCM inputs when only decoder B and C inputs are pulled low. This will complete high/low check of all 4 BCM inputs.
3. This step is to check gear selector switch problem in other gear ranges.
4. Checks to see if code is due to discrepancy between ECM and BCM inputs.
5. Checks for short to ground in gear selector switch to BCM circuits.
6. Checks for open in gear selector switch to BCM circuits.
7. Circuit shorted to ground will result in a "0" for the circuit.
8. Checks for open gear selector sensor ground.
9. Circuit with open will result in a "1" for the circuit.

Manipulate related ECM and BCM wiring in each gear range while looking for a change in BD41 or EI74 values to check for intermittent open or short to ground. Also check terminals for good contact at ECM, BCM and gear selector switch. If good contact exists and Code B127 continues to set, replace BCM.

Code B127, Gear Selector Switch Circuit (Toronado 1 of 2). Scheme 214

Code B127, Gear Selector Switch Circuit (Toronado 2 of 2). Scheme 215

Circuit Description

The purpose of TCC is to eliminate the power loss of torque converter stage when vehicle is in "cruise" condition. This allows the use of an automatic transmission with the fuel economy of a manual transmission.

Fused battery ignition power is supplied to TCC solenoid through the TCC brake switch.

The ECM will engage TCC by grounding circuit No. 422 to energize the TCC solenoid.

Engagement of torque converter clutch will be executed under the following conditions

1. Vehicle speed above 24 MPH.
2. Engine temperature above 149°F (65°C).
3. Steady TPS reading (not changing-steady road speed).
4. Brake switch closed.
5. Transmission in 3rd or 4th gear.

Test Description

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

1. Check continuity through the brake switch and TCC solenoid.
2. Check ability of ECM to energize the TCC solenoid. Grounding the diagnostic connector should energize the relay and cause the light to go out.
3. This test by-passes the TCC solenoid and checks for an open or short in circuit No. 422.

Solenoid coil resistance must measure more than 20 ohms. Less resistance ill cause early failure of the ECM "DRIVER". Using an ohmmeter, check solenoid coil resistance of all ECM-controlled solenoids and relays before replacing ECM. Replace any solenoid or relay that measures less than 20 ohms resistance.

TCC Electrical Diagnosis Flow Chart (2.5/2.8L Light Trucks & Vans). Scheme 216

Chart C-8, Torque Converter Clutch 2.5L & 2.8L Light Trucks & Vans. Scheme 217

TCC Electrical Diagnosis Schematic (2.5L/2.8L Light Trucks & Vans). Scheme 218

The purpose of TCC is to eliminate the power loss of torque converter stage when vehicle is in "cruise" condition. This allows the use of an automatic transmission with the fuel economy of a manual transmission.

Fused battery ignition power is supplied to TCC solenoid through the TCC brake switch.

The ECC will engage TCC by grounding circuit No. 422 to energize the TCC solenoid.

Engagement of torque converter clutch will be executed under the following conditions

1. Vehicle speed above 30 MPH.
2. Engine temperature above 149°F (65°C).
3. Steady TPS reading (not changing-steady road speed).
4. Brake switch closed.
5. Transmission in 3rd or 4th gear.

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

1. Glowing test light indicates that battery voltage and continuity through TCC Solenoid are okay.
2. Checks for vehicle speed sensor (VSS) signal to ECM, using a "SCAN" tester.
3. Checks for 4th gear signal to ECM. This signal will not prevent TCC engagement, but could cause a change in engage/disengage speed points.

Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure of the ECM "DRIVER". Using an ohmmeter, check solenoid coil resistance of all ECM-controlled solenoids and relays before replacing ECM. Replace any solenoid or relay that measures less than 20 ohms resistance.

TCC Elect. Diagnosis Flow Chart (4.3/5.0/5.7L Trucks Under 8500 GVW). Scheme 219

Use A "Scan" Tool To Check The Following & Correct If Necessary

1. Coolant Temperature
2. TPS
3. VSS
4. Codes - If 24 Is Present, See Code Chart 24

Also, Perform Mechanical Checks, Such As Linkage, Oil Level, Etc., Before Using This Chart

Chart C-8, Torque Converter Clutch 4.3L, 5.0L, 5.7L Light Trucks & Vans (1 Of 2). Scheme 220

Chart C-8, Torque Converter Clutch 4.3L, 5.0L, 5.7L Light Trucks & Vans (2 Of 2). Scheme 221

TCC Elect. Diagnosis Schematic (4.3/5.0/5.7L Light Trucks Under 8500 GVW). Scheme 222

When accelerator pedal is fully depressed, manifold vacuum drops, causing MAP sensor signal voltage to increase to about 4 volts. The ECM responds by grounding circuit No. 422 to energize downshift control relay. The downshift control relay then sends battery voltage to detent solenoid that causes a forced transmission downshift.

If problem is diagnosed as being an internal transmission problem, perform transmission service.

Relay coil resistance must measure more than 20 ohms. Less resistance will cause early failure of the ECM "DRIVER". Using an ohmmeter, check solenoid coil resistance of all ECM-controlled solenoids and relays before replacing ECM. Replace any solenoid or relay that measures less than 20 ohms resistance.

THM 400 Downshift Control Flow Chart (Light Trucks & Vans). Scheme 223

THM 400 Downshift Control Light Trucks & Vans. Scheme 224

THM 400 Downshift Control Schematic (Light Trucks & Vans). Scheme 225

The ECM supplies and monitors 12-volt signal on circuit No. 437. Circuit No. 437 connects Vehicle Speed Sensor (VSS), that alternately grounds circuit No. 437 when drive wheels are turning. This pulsing action takes place about 2000 times per mile, and the ECM calculates vehicle speed based on time between "pulses".

"SCAN" tester reading should closely match speedometer reading with drive wheels turning.

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

Code 24 will set if the following conditions exist for at least 3 seconds

1. Circuit No. 437 voltage is constant.
2. Engine speed is 900-4400 RPM.
3. Less than 2% throttle opening.
4. Low load condition (low airflow).
5. Transmission not in Park or Neutral.

The above conditions are met during a road load deceleration.

1. This monitors ECM voltage on circuit No. 437. With wheels turning, pulsing action will result in varying voltage. Variation will be greater at low wheel speeds to an average of 4-6 volts at about 20 MPH.
2. A voltage of less than one volt at ECM connector indicates that circuit No. 437 is shorted to ground. Disconnect circuit No. 437 at VSS. If voltage now reads above 10 volts, VSS is faulty. If voltage remains less than 10 volts, circuit No. 437 wire 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 faulty VSS.
4. This is a normal voltage that indicates a possible intermittent condition.

"SCAN" tester reading should closely match speedometer reading with drive wheels turning.

See PARK/NEUTRAL SWITCH DIAGNOSIS chart if vehicle is equipped with automatic transmission.

If Park/Neutral switch is okay, see INTERMITTENT TROUBLE CODES in appropriate CCC TESTS W/O CODES article in ENGINE PERFORMANCE.

Code 24 VSS Flow Chart & Schematic (Light Trucks & Vans). Scheme 226

Code 24, Vehicle Speed Sensor Light Trucks & Vans. Scheme 227

The P/N switch contacts are closed to ground in Park or Neutral, and open in all Drive ranges. The ECM supplies ignition voltage, through a current limiting resistor, to circuit No. 434. The ECM senses a closed switch when voltage on circuit No. 434 drops to less than one volt. The ECM uses P/N signal as one of the inputs to control idle air, VSS diagnostics, and EGR flow.

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

1. Checks for closed switch to ground in Park position. Different makes of "SCAN" testers will read P/N signal differently. Refer to tester's instruction manual for type of display used for specific tester.
2. Checks for an open switch in Drive or Reverse.
3. Be sure "SCAN" tester indicates Drive, even while wiggling shifter, to test for an intermittent or misadjusted switch in Drive.

If circuit No. 434 indicates P/N switch grounded while in Drive, EGR would be inoperative, resulting in possible detonation.

If circuit No. 434 always indicates Drive (open), a drop in idle may exist when gear selector is moved into Drive.

Chart C-1A Flow Chart & Schematic (Light Trucks & Vans). Scheme 228

Chart C-1A, Park/Neutral Switch Light Trucks & Vans. Scheme 229