Diagnosis - Torque Converter Clutch - Trucks GMC Cab & Chassis 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 are included. Other diagnostic codes may appear while performing TCC electrical diagnosis. For complete information on General Motors Computerized Engine Control systems see COMPUTERIZED ENGINE CONTROL articles in the ENGINE PERFORMANCE section.

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 is activated, the torque converter clutch is applied which results in a straight through mechanical coupling from engine to transmission. When TCC solenoid is deactivated, the torque converter clutch is released which allows the torque converter clutch to operate in a conventional manner.

Scheme 117

TCC CONTROL COMPONENTS

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

Vehicle Speed Sensor (VSS)

Contains the TCC apply and regulator valves. Apply valve determines method of fluid feed to torque converter assembly in order to enable or disable clutch mechanism.

Brake Switch

The brake switch releases converter clutch when brakes are applied to prevent engine from stalling.

Coolant Temperature Sensor

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

Electronic Control Module (ECM)

The ECM receives and processes inputs from vehicle speed sensor, coolant temperature sensor, throttle position sensor, 3rd or 4th gear switch, and brake switch to determine application of torque converter clutch. The ECM controls application of torque converter clutch by grounding TCC solenoid circuit.

TCC Solenoid Assembly

Energizes to redirect transaxle fluid to the converter clutch apply valve in the auxiliary control valve assembly.

Throttle Position Sensor (TPS)

Provides the ECM with throttle position information. TCC operation is prevented below a specific signal level.

3rd & 4th Gear Switch

The 3rd and 4th gear switches prevent TCC operation until direct drive (3rd and/or 4th gear) is obtained.

Vacuum Sensor

Sends engine vacuum (load) information to ECM.

This sensor sends vehicle speed information to ECM. Vehicle speed must be above a certain value before TCC can be applied. This sensor is located in instrument cluster, behind speedometer.

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.
4. Damaged or worn linkage.

When diagnosing Converter Clutch problems, ensure engine and vacuum systems are in perfect operating order.

CONVERTER CLUTCH TROUBLESHOOTING

TURBO HYDRA-MATIC 180C

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.
4. Damaged or worn linkage.

TURBO HYDRA-MATIC 180C TROUBLE SHOOTING

TURBO HYDRA-MATIC 200C

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.
4. Damaged or worn linkage.

TURBO HYDRA-MATIC 200C TROUBLE SHOOTING

TURBO HYDRA-MATIC 200-4R

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.
4. Damaged or worn linkage.

TURBO HYDRA-MATIC 200-4R TROUBLE SHOOTING

TURBO HYDRA-MATIC 400

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
4. Damaged or worn linkage.

TURBO HYDRA-MATIC 400 TROUBLE SHOOTING

TURBO HYDRA-MATIC 700-R4

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
4. Damaged or worn linkage.

TURBO HYDRA-MATIC 700-R4 TROUBLE SHOOTING

DIAGNOSTIC TOOLS

The TCC system does not require special tools for diagnosis. A tachometer, a test light, ohmmeter, digital voltmeter with 10 megohms 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).

Note. Special "SCAN" testers can be used to read trouble codes and check voltages in the system. These tools can save a great deal of time, but are not required. Refer to tester manual for operating procedures. Also see "SCAN" portion of test chart(s).

ENTERING DIAGNOSTIC MODE

The ECM stores component failure information under a related trouble code which can be recalled for diagnosis and repair. When recalled, these codes will be displayed by flashes of the "CHECK ENGINE"/"SERVICE ENGINE SOON" light.

It is NOT necessary to enter diagnostic mode to use TCC test chart(s). It will be necessary to enter ECM diagnostic mode to verify the presence of any codes.

Scheme 118

1. To enter diagnostic mode, turn ignition on but do not Start engine. "CHECK ENGINE"/"SERVICE ENGINE SOON" light should glow. Locate Assembly Line Communication Link (ALCL) connector attached to ECM wiring harness under instrument panel. Insert jumper wire across diagnostic mode test terminal "B" and ground terminal "A". (Scheme 118) CAUTION: Inserting spade lug in terminals of ALCL connector grounds "TEST" terminal lead. Do not ground ALCL connector until after ignition is on.
2. "CHECK ENGINE"/"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. Be sure 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 from the battery for 10 seconds and then reconnect it. In either case, be sure the ignition switch is in the "OFF" position before removing battery voltage, for a voltage spike could occur if the switch is in the "ON" position.

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 will refer to corresponding vehicle speed sensor (Code 24), and park/neutral switch test charts.

CHART C-8A TCC ELECTRICAL DIAGNOSIS - 2.5L & 2.8L

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

The ECM will engage TCC when vehicle speed is above 24 MPH engine at normal operating temperature (above 149°F/65°C), throttle position sensor output not changing (indicating a steady road speed) brake switch closed and vehicle in 3rd or 4th gears.

FLOWCHART - CHART C-8A (1 of 2). Scheme 119

FLOWCHART - CHART C-8A (2 of 2). Scheme 120

1. Checks continuity through brake switch and TCC solenoid.
2. Grounding diagnostic terminal should energize relay and cause light to go out. This test checks capability of ECM to control solenoid.
3. This test by-passes TCC solenoid and checks for an open or short in circuit No. 422.
4. Solenoids are turned on or of by ECM internal electronic switches called drivers. Each driver is part of a group ot four called quad-drivers. Failure of one can damage another driver within a set.

Note. Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure of ECM driver. Using an ohmmeter check solenoid coil resistance of all ECM controlled solenoids and relays before installing a replacement ECM. Replace any solenoid or relay that measures less than 20 ohms.

CHART C-8 TCC ELECTRICAL DIAGNOSIS - 4.3L, 5.0L & 5.7L

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

The ECM will engage TCC when vehicle speed is above 30 MPH, engine at normal operating temperature (above 149°F/65°C), throttle position sensor output not changing (indicating a steady road speed), brake switch closed, and 4th gear switch closed.

FLOWCHART - CHART C-8 (1 of 2). Scheme 121

FLOWCHART - CHART C-8(1 of 2). Scheme 122

1. If test light comes on it indicates battery voltage and continuity throguh TCC solenoid in okay.
2. This test checks Vehicle Speed Sensor (VSS) signal to ECM. Voltage should vary from below 2 volts to over 8 volts.
3. This test checks 4th gear switch signal to ECM. This signal will not prevent TCC engagement, but could cause a change in engage and disengage speeds.

Note. Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure or ECM driver. Using an ohmmeter, check 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.

CODE 24, VEHICLE SPEED SENSOR (VSS)

The ECM applies and monitors 12 volts to circuit No. 437 which connects to Vehicle Speed Sensor (VSS). The VSS alternately grounds circuit No. 437 when the 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 SCAN tool reading should closely match with speedometer reading with drive wheels turning.

Code 24 will set if: circuit No. 437 voltage is constant, engine speed is between 900 and 4400 RPM, there is less than 2% throttle opening, there is a low load condition (low airflow) or if transnnission is not in park or neutral. All conditions must be met for at least 3 seconds. These conditions are met during a road load deceleration.

Note. Disregard CODE 24 if set while drive wheels are not turning.

FLOWCHART - CODE 24. Scheme 123

1. This test monitors the ECM voltage on circuit No. 437. With wheels turning, the pulsing action will result in a varying voltage. The 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 1 volt at ECM connector indicates that circuit No. 437 wire is shorted to ground. Disconnect circuit 437 at VSS. If voltage now reads above 10 volts, the VSS is faulty. If voltage remains less than 10 volts, then circuit No 437 wire is grounded. If 437 is not grounded, check for a faulty ECM connector or ECM.
3. A steady 8-12 vats at ECM connector indicates circuit 437 is open or a faulty VSS.
4. This is normal voltage which indicates a possible intermittent condition.

Note. SCAN reading should closely match with speedometer reading, with drive wheels turning. Check park/neutral switch diagnosis chart if vehicle if equipped with automatic transmission.

PARK/NEUTRAL SWITCH TEST CHART

Park/Neutral switch contacts 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. The ECM also senses a closed switch when the voltage on circuit No. 434 drops to less than one volt. ECM uses the Park/Neutral signal as one of the inputs to control the following Idle Air Control (IAC), Vehicle Speed Sensor (VSS) and Exhaust Gas Recirculation (EGR).

FLOWCHART - PNP SWITCH TEST. Scheme 124

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

Note. If circuit No. 434 indicates P/N (grounded), while in drive range, the EGR would be inoperative, resulting in possible detonation. If circuit No. 434 always indicates drive (open), a drop in the idle may exist when the gear selector is moved into drive range.