Automatic Transmission - Diagnosis - 4l80-e Chevrolet Forward Control P30

APPLICATION

THM 4L80-E APPLICATION

VEHICLE CODE DESIGNATION

1991 SERIES CODE DESIGNATIONS

1992 SERIES CODE DESIGNATIONS

DESCRIPTION

The 4L80-E transaxle uses 2 electric shift solenoids to control transmission upshifts and downshifts. In addition, a force motor (solenoid) controls hydraulic line pressure, and a Torque Converter Clutch (TCC) solenoid controls TCC application. Solenoid is turned on and off by the Powertrain Control Module (PCM) or Transmission Control Module (TCM). The PCM/TCM has on-board self-diagnostics to help identify any parts or circuits that may need further testing.

Note. For testing information on converter clutch lock-up control, see AUTO TRANS DIAGNOSIS - GM TORQUE CONVERTER CLUTCH .

OPERATION

Shift solenoid holds hydraulic pressure when is on and releases pressure when it is off. This action controls the shift valves inside valve body. By switching one or both solenoids on or off, different combinations of clutches, sprags and bands are operated. See CLUTCH & BAND APPLICATION CHART table under ELECTRONIC TESTING.

PCM/TCM

Note. Models with gasoline engines use a Powertrain Control Module (PCM) computer. Models with diesel engines use a Transmission Control Module (TCM) computer. These computers control TCC, force motor (hydraulic pressure) and shifting solenoids "A" and "B".

The PCM/TCM is located behind glove box on all vehicles except "G" Series. On "G" Series, PCM/TCM is under driver's seat. PCM/TCM controls TCC, force motor (hydraulic pressure) and shifting solenoids "A" and "B". In addition, PCM also controls ignition, fuel and emission devices related to the engine.

The PCM/TCM receives electronic signals from sensors and switches. These signals help the PCM/TCM determine when to operate various relays and solenoids related to engine and transmission components.

SENSORS & SWITCHES

The PCM/TCM controls upshifts and downshifts based on coolant temperature, transmission temperature, system voltage, throttle position, transmission oil pressure switches, and transmission output and input speed sensors. (Scheme 366) The system includes several other switches and sensors that are used for engine control (gasoline engines). For additional information and testing of engine components, see appropriate article in ENGINE PERFORMANCE.

Shift Solenoids "A" & "B"

Transmission is shifted up or down by 2 electric solenoids. Both solenoids are located on valve body. (Scheme 366) Ignition power is supplied to each solenoid by the transmission fuse. Solenoid "A" controls hydraulic pressure to 1-2 and 3-4 shift valves. Solenoid "B" controls hydraulic pressure to 2-3 shift valve.

Force Motor

Force motor solenoid has a spool valve and operates pressure regulator valve. (Scheme 366) The computer sends a frequency signal to the force motor to regulate hydraulic line pressure. The frequency signal (duty cycle) is measured with a dwell meter or lab scope. When the duty cycle is zero, line pressure is at maximum, and force motor draws zero amp. When the duty cycle is 40%, line pressure is at minimum, and force motor draws 1.1 amps at 4-5 volts.

TCC Solenoid

This solenoid is used to control TCC apply valve. The computer sends a frequency signal to the TCC solenoid to gradually apply or release the TCC. (Scheme 366)

Scheme 366

SELF-DIAGNOSTICS

The PCM/TCM constantly monitors all electrical circuits. If the PCM/TCM detects circuit problem(s) or out-of-range sensor(s), a trouble code(s) will be recorded in computer memory. If problem continues for a preset time, the TRANS or SERVICE ENGINE SOON light will glow.

If the TRANS or SERVICE ENGINE SOON light is always on, trouble code(s) is currently being detected. If the TRANS or SERVICE ENGINE SOON light is off, but PCM/TCM has detected a circuit or sensor problem, trouble code(s) will be stored in computer memory.

Stored trouble codes may be retrieved from PCM/TCM memory using "Scan" tool or TRANS or SERVICE ENGINE SOON light. See appropriate RETRIEVING CODES procedure under ELECTRONIC SELF-DIAGNOSTICS .

Note. For complete PCM/TCM testing and diagnosis, see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section

1. For Diesel Vehicles, see «TESTS W/CODES - DIESEL»(/chevrolet/forward-control-p30/1985-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-diesel)
2. For Transmission Codes, see «TESTS W/CODES - TRANSMISSION»(/chevrolet/forward-control-p30/1985-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-transmission)
3. For V6 Equipped Vehicles, see «TESTS W/CODES - V6»(/chevrolet/forward-control-p30/1985-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-v6)
4. For V8 Equipped Vehicles, see «TESTS W/CODES - V8»(/chevrolet/forward-control-p30/1985-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-v8)

ELECTRONIC SELF-DIAGNOSTICS

Note. To test electronic control of transmission solenoids without using self-diagnostics, go to COMPONENT TEST CHARTS (NO CODES) under ELECTRONIC TESTING . After repairs are made, trouble codes should be erased from computer memory. See CLEARING TROUBLE CODES .

Scheme 367

1. Turn ignition on. DO NOT start engine. TRANS or SERVICE ENGINE SOON light should glow. Locate Assembly Line Data Link (ALDL) connector under dash, on driver's side of vehicle. Turn ignition on with engine not running. Connect jumper wire from terminal "B" (diagnostic terminal) to terminal "A" (ground terminal) of ALDL connector. (Scheme 367) NOTE: Connecting terminals "A" and "B" of ALDL connector with engine running will cause fuel injected vehicles to enter field service mode. The TRANS or SERVICE ENGINE SOON light will not flash codes if this is done.
2. TRANS or SERVICE ENGINE SOON light should begin flashing codes. Each code will be repeated 3 times. Code 21 is identified by 2 flashes, a short pause followed by one flash; Code 53 is identified by 5 flashes, a short pause followed by 3 flashes. Trouble codes are separated by slightly longer pauses.
3. Trouble codes are displayed in numerical order. Each code is displayed 3 times. Codes will continue to repeat as long as ALDL test terminal is grounded.
4. If codes are not flashed, or TRANS or SERVICE ENGINE SOON light does not glow, self-diagnostics will not work. See «CHART A-1»(/chevrolet/forward-control-p30/1985-1999/remont/automatic-trans/#automatic-transmission-diagnosis-4l80-e) under DIAGNOSTIC CHARTS. If TRANS or SERVICE LIGHT SOON light glows steadily, see «CHART A-2»(/chevrolet/forward-control-p30/1985-1999/remont/automatic-trans/#automatic-transmission-diagnosis-4l80-e) under DIAGNOSTIC CHARTS. To exit diagnostic mode, turn ignition off, and remove jumper wire from ALDL connector.

Note. Trouble codes will be recorded at various operating times. Some codes require operation of sensor or switch for 5 seconds; others may require operation for 5 minutes or longer at normal operating temperature, road speed and load. Therefore, some codes may not set in a service bay operational mode, but may require road testing vehicle in order to duplicate condition under which code will set.

RETRIEVING CODES (WITH "SCAN" TOOL)

Note. To read trouble codes and check system voltages on serial data line, plug "Scan" tool into ALDL.

The "Scan" tool is a specialized tester which, when plugged into ALDL, can be used to diagnose on-board computer control systems by providing instant access to circuit voltage information without need to crawl under dash or hood to backprobe sensors and connectors.

"Scan" tools may also furnish information on status of output devices (solenoids and relays). However, status parameters are only an indication that output signals have been sent to devices by the control module. It does not indicate if devices have responded properly to that signal. This will need to be checked at output device using a voltmeter or test light.

Note. Code 12 should always exist when ALDL is grounded with key on and engine off, but may not be indicated by all makes of "Scan" tools.

If trouble code is not present, this is not an indication that is no problem. Driveability-related problems with codes displayed occur about 20 percent of the time, while driveability problems without codes occur about 80 percent of the time.

Out-of-specification sensors WILL NOT set trouble code, but WILL cause driveability problems. Using "Scan" tool is the easiest method of checking sensor specifications and other data parameters. Intermittent wiring problems may be identified by wiggling wiring harnesses and connections (key on, engine off) while observing "Scan" tool.

Note. If erroneous voltage signals are suspected, it will be necessary to verify tester information using digital voltmeter and wiring schematic. If non-existent codes are displayed, turn ignition off, remove tester, turn ignition on, and ground ALDL test terminal "B". The same codes should be retrieved whether "Scan" tool or TRANS or SERVICE ENGINE SOON light is used.

TROUBLE CODE DEFINITION

PCM/TCM TROUBLE CODE DEFINITION

Note. Only transmission-related trouble codes are listed. If other trouble codes are present, see appropriate article in the ENGINE PERFORMANCE section.

HARD OR INTERMITTENT TROUBLE CODE DETERMINATION

During any diagnostic procedure, it must be determined if codes are hard failure codes or intermittent failure codes. A hard failure indicates that a problem is currently present. Diagnostic charts do not usually provide intermittent code diagnosis. To determine hard codes and intermittent codes, proceed as follows

1. Manually enter diagnostic mode. Record all stored trouble codes. Exit diagnostic mode, and clear trouble codes. See «CLEARING TROUBLE CODES»(/chevrolet/forward-control-p30/1985-1999/remont/automatic-trans/#automatic-transmission-diagnosis-4l80-e__clearing-trouble-codes) .
2. Apply parking brake, and place transmission in Neutral or Park. Block drive wheels, and start engine. TRANS or SERVICE ENGINE SOON light should go out. Operate warm engine at specified curb idle for 2 minutes, and note TRANS or SERVICE ENGINE SOON light.
3. If TRANS or SERVICE ENGINE SOON light does not come on, codes are intermittent failures. If TRANS or SERVICE ENGINE SOON light comes on, manually enter diagnostic mode. Record trouble codes. If same codes reappear, they are hard failure codes. It may be necessary to road test vehicle in order to reset hard failure codes.

CLEARING TROUBLE CODES

Turn ignition switch to ON position, and ground diagnostic test terminal "B" at ALDL connector. Turn ignition switch to OFF position, and remove control module fuse from fuse block for 30 seconds. Install fuse. Remove diagnostic terminal ground lead. If fuse cannot be located, pigtail at battery can be disconnected. When power to ECM is removed, poor driveability may occur until control module relearns operating parameters.

DIAGNOSTIC CHARTS

The following charts include flow charts, testing information and related wiring diagram. For complete transaxle wiring diagrams, see WIRING DIAGRAMS . For additional engine diagnostic information, see appropriate article in the ENGINE PERFORMANCE section.

Note. DIAGNOSTIC AIDS in charts may help diagnose trouble codes when problem cannot be identified through circuit checks.

Scheme 368

Note. Test numbers refer to numbers on diagnostic chart.

1. If ECM-B fuse is blown, refer to «WIRING DIAGRAMS»(/chevrolet/forward-control-p30/1985-1999/remont/automatic-trans/#automatic-transmission-diagnosis-4l80-e) at end of article to identify related circuits.
2. Using a 12-volt test light, connect clip end to 12 volts. Probe each PCM/TCM ground circuit and ensure continuity to ground is present.

Diagnostic Aids

If engine runs okay, check for faulty light bulb. Check for open circuit 419 or blown ALT fuse. A blown ALT fuse will also cause instrument panel-mounted warning lights not to work.

Scheme 369

Scheme 370

Note. Test numbers refer to numbers on diagnostic chart.

1. If Code 12 does not flash, ensure "Scan" tool is working by testing another vehicle. If "Scan" tool and circuit 1061 are okay, PCM/TCM or PROM/MEM-CAL may be cause of no ALDL data.
2. If TRANS or SERVICE ENGINE SOON light goes off (with PCM/TCM disconnected), circuit 419/1234 is not shorted to ground.
3. This step checks for open diagnostic circuit 451.
4. TRANS or SERVICE ENGINE SOON light control circuit is okay. Replace PCM/TCM and/or PROM/MEM-CAL.

Scheme 371

Scheme 372

Note. This chart assumes engine cooling system is functioning properly (not overheating). Test numbers refer to numbers on diagnostic chart.

1. This checks if conditions for Code 14 still exist. Code 14 indicates control module has sensed low coolant sensor voltage signal (high temperature) at control module terminal for one second.
2. This tests for grounded sensor signal line between control module and coolant sensor.

After engine is started, temperature should rise steadily to about 190°F (88°C), then stabilize when thermostat opens. At normal operating temperature, signal voltage at control module terminal should be 1.5-2.0 volts. Measure sensor resistance to check for shifted calibration. See TEMPERATURE-TO-RESISTANCE VALUES (CODE 14) table.

TEMPERATURE-TO-RESISTANCE VALUES (CODE 14)

Scheme 373

CODE 15 - COOLANT TEMPERATURE SENSOR LOW TEMPERATURE INDICATED (SIGNAL VOLTAGE HIGH)

(Scheme 370)for Component Diagram.

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

1. This checks if conditions for Code 15 still exist. Code 15 indicates control module has sensed high resistance in coolant sensor circuit. This could be due to high resistance (low temperature) or high voltage at coolant sensor terminal at control module for one second.
2. This test simulates conditions for Code 14. If control module recognizes low voltage signal, "Scan" tool will display temperature greater than 266°F (130°C), indicating control module and wiring are not at fault.
3. This test determines if coolant sensor ground or signal circuit is open. There should be 5 volts present at sensor connector.

After engine is started, temperature should rise steadily to about 190°F (88°C) then stabilize when thermostat opens. At normal operating temperature, voltage at control module sensor signal line should be 1.5-2.0 volts. Measure sensor resistance to check for shifted calibration. See TEMPERATURE-TO-RESISTANCE VALUES (CODE 15) table.

TEMPERATURE-TO-RESISTANCE VALUES (CODE 15)

Scheme 374

Scheme 375

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if code is result of a hard failure or an intermittent failure.
2. This test simulates conditions for Code 22. If control module recognizes state change, control module and wiring are okay.
3. This step isolates faulty sensor, control module or open sensor ground circuit. If sensor ground is shared by another sensor, there may be an accompanying code related to that sensor.

"Scan" tool displays throttle position in volts. Closed throttle voltage should be low. As throttle angle increase, voltage should increase gradually to about 4.5 volts at a steady rate.

Scheme 376

CODE 22 - THROTTLE POSITION SENSOR SIGNAL VOLTAGE LOW

(Scheme 370)for Component Diagram.

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

1. This test checks if code is result of a hard failure or an intermittent failure.
2. This test simulates conditions for Code 21. If control module recognizes state change, control module and wiring are okay.
3. This simulates high signal voltage to check for open in TPS signal line to control module. "Scan" tool should recognize signal and display high TPS voltage.

"Scan" tool displays throttle position in volts. Closed throttle voltage should be low. As throttle angle increases, voltage should increase gradually to about 4.5 volts at a steady rate. Open or short to ground in circuit 416 or 417 will set Code 22.

Scheme 377

Scheme 378

The speed sensor, which is a Permanent Magnet (PM) generator, provides Digital Ratio Adapter Control (DRAC) with vehicle speed information. PM generator, mounted in transmission, produces a pulsing voltage signal whenever vehicle speed is greater than 3 MPH. Voltage level and pulse increase with vehicle speed. DRAC converts PM generator signal to pulsing signal by grounding circuit to PCM/TCM 2000 times per mile. Control module uses this pulsing signal in calculations to determine vehicle adjustments.

Code 24 will set under following conditions: vehicle speed is less than 20 MPH, transmission is not in Park or Neutral, and engine speed is greater than 3000 RPM. All of these conditions must be met for 1.5 seconds. PM generator only produces voltage signal if drive wheels are turning faster than 3 MPH.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step tests for voltage variation while wheels are turning. Voltage will be low at low wheel speeds (4-6 volts at 20 MPH).

Very carefully check the pass-through connector at transmission.

Scheme 379

Scheme 380

The speed sensor, which is a Permanent Magnet (PM) generator, provides Digital Ratio Adapter Control (DRAC) with vehicle speed information. PM generator, mounted in transmission, produces a pulsing voltage signal whenever vehicle speed is more than 3 MPH. Voltage level and pulse increase with vehicle speed. DRAC converts PM generator signal to a pulsing signal by grounding circuit 437 (Brown wire) 2000 times per mile. Control module uses this signal in calculations to determine vehicle adjustments.

Code 24 will set under following conditions: vehicle speed is less than 20 MPH, transmission is not in Park or Neutral, and engine speed is more than 3000 RPM. All of these conditions must be met for 1.5 seconds. PM generator only produces voltage signal if drive wheels are turning faster than 3 MPH.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step tests for voltage variation while wheels are turning. Voltage will be low at low wheel speeds (4-6 volts at 20 MPH).
2. This step tests operation of output speed sensor.
3. This step checks for faulty DRAC, or open circuits 821 and 822.

Very carefully check the pass-through connector at transmission. If input sensor is not working at start-up, output sensor will read zero. If Code 24 is set in computer memory, "Scan" tool will read engine RPM (input sensor signal).

Scheme 381

Scheme 382

The speed sensor, which is a Permanent Magnet (PM) generator, provides Digital Ratio Adapter Control (DRAC) with vehicle speed information. PM generator, mounted in transmission, produces a pulsing voltage signal whenever vehicle speed is more than 3 MPH. Voltage level and pulse increase with vehicle speed. DRAC converts PM generator signal to a pulsing signal by grounding circuit 437 (Brown wire) 2000 times per mile. Control module uses this signal in calculations to determine vehicle adjustments.

Code 24 will set under following conditions: vehicle speed is zero, transmission is not in Park or Neutral, engine speed is more than 3000 RPM, and PCM/TCM input circuit 437 is constant. All of these conditions must be met for 1.5 seconds. PM generator only produces voltage signal if drive wheels are turning faster than 3 MPH.

Note. Test numbers refer to numbers on diagnostic chart.

1. This tests for voltage variation while wheels are turning. Voltage will be low at low wheel speeds (4-6 volts at 20 MPH).
2. This step determines whether VSS assembly is faulty, circuit 437 is grounded, or PCM/TCM connector or PCM/TCM is faulty.
3. This signal indicates an open circuit 437 or faulty DRAC.
4. This is a normal voltage signal.

Using "Scan" tool, check for proper signal in Drive while wiggling wiring. Ensure all connectors are good. Very carefully check the pass-through connector at transmission.

Scheme 383

Scheme 384

The speed sensor, which is a Permanent Magnet (PM) generator, provides PCM/TCM with vehicle speed information. PM generator, mounted in transfer case, produces a pulsing voltage signal whenever vehicle speed is more than 3 MPH. Control module uses this signal in calculations to determine vehicle adjustments.

Code 24 will set under following conditions: vehicle speed is less than 20 MPH, transmission is not in Park or Neutral, and engine speed is more than 3000 RPM. All of these conditions must be met for 1.5 seconds. PM generator only produces voltage signal if drive wheels are turning faster than 3 MPH.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step tests for voltage variation while wheels are turning. Voltage will be low at low wheel speeds (4-6 volts at 20 MPH).
2. This step tests operation of output sensor.

Very carefully check the pass-through connector at transmission. If input sensor is not working at start-up, output sensor will read zero.

Scheme 385

Scheme 386

Note. Test numbers refer to numbers on diagnostic chart.

1. This step tests for proper operation of pressure switches.
2. This step tests for correct voltage from PCM/TCM to transmission pass-through connector.
3. This step tests for short to ground in any one of 3 pressure switch circuits.

Code 28 will set if an illegal switch combination is detected. See PSM COMBINATION CHART table. Check transmission pass-through connector connections.

PSM COMBINATION CHART

Scheme 387

Scheme 388

Code 39 will set when TCC is commanded by PCM/TCM, transmission is in high gear, engine speed-to-vehicle speed ratio does not indicate TCC has engaged and 2nd or 3rd gear is indicated. All these conditions must be met for more than 2 seconds.

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

1. This step tests for poor connection at transmission pass-through connector.
2. This step tests for power to transmission pass-through connector.
3. This step tests for PCM/TCM control of TCC.

Clear codes. If Code 39 reappears, problem may be inside torque converter or transmission. Code 39 will only set in 3rd gear.

Scheme 389

Scheme 390

Control module monitors voltage on battery feed circuit. If control module detects that voltage is greater than 19.2 volts for more than 2 seconds, force motor will shut off, TCC will be released, and transmission will shift to 2nd gear.

Note. Test numbers refer to numbers on diagnostic chart. Starting engine with battery charger connected may set Code 53.

1. Normal system charging voltage is 10-17 volts.
2. This step checks whether generator, circuit 440 or PCM/TCM is the cause of Code 53.
3. This step tests alternator output to determine proper operation of voltage regulator. Increase engine speed to a moderate level, and measure voltage across battery terminals. If reading is greater than 19.2 volts, service alternator.

Check for poor connections or damaged harness. Also, check for intermittent condition by starting engine and wiggling connection while monitoring battery voltage on "Scan" tool. If voltage status changes abruptly, check for loose connections.

Scheme 391

Scheme 392

Code 58 indicates PCM/TCM has sensed low sensor voltage signal (high temperature) at PCM/TCM terminal for one second.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks if conditions for Code 58 still exist.
2. This step tests for grounded sensor signal line between control module and coolant sensor.

After transmission has been in operation, temperature should rise steadily to about 212°F (100°C) then stabilize. At normal operating temperature, voltage at PCM/TCM signal line should be 1.5-2.0 volts. Measure sensor resistance to check shifted calibration. See TEMPERATURE-TO-RESISTANCE VALUES (CODE 58) table.

TEMPERATURE-TO-RESISTANCE VALUES (CODE 58)

Scheme 393

Code 59 Circuit Diagram. Scheme 394

Code 59 indicates PCM/TCM has sensed high resistance in transmission sensor circuit. This could be due to high resistance (low temperature) or high voltage at transmission sensor terminal at PCM/TCM for one second.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks if conditions for Code 59 still exist.
2. This test simulates conditions for Code 58. If PCM/TCM recognizes low voltage signal, "Scan" tool will display temperature greater than 304°F (151°C), indicating control module and wiring are not at fault.
3. This test determines whether transmission sensor ground or signal circuit is open. There should be 5 volts present at transmission sensor connector.

After transmission has been in operation, temperature should rise steadily to about 212°F (100°C) then stabilize. At normal operating temperature, voltage at PCM/TCM sensor signal line should be 1.5-2.0 volts. Check sensor for shifted calibration. See TEMPERATURE-TO-RESISTANCE VALUES (CODE 59) table.

TEMPERATURE-TO-RESISTANCE VALUES (CODE 59)

Scheme 395

Scheme 396

Note. Test numbers refer to numbers on diagnostic chart.

1. Code 68 will set under following conditions: transmission is not in Park or Neutral, TCC slips in 4th gear, transmission is in 4th gear, and TCC is locked on. All conditions must be met for 2 seconds.
2. This step checks transmission signal being sent to PCM/TCM.
3. This step checks for engine RPM signal being sent to PCM/TCM.

Check transmission pass-through connector. Code 68 will set if transmission defaults to 2nd gear. If problems are still present, check for possible internal transmission problems.

Scheme 397

Scheme 398

PCM/TCM monitors signal return amperage. If return amperage varies more than .16 amp from amperage sent by PCM/TCM, Code 73 will be set. If this occurs, force motor is disabled, and maximum line pressure occurs.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks control of force motor by PCM/TCM.
2. Voltage should be present.
3. This step checks if problem is inside transmission.
4. This step checks for short to ground.
5. This step checks for high resistance inside transmission.

Check transmission pass-through connector and PCM/TCM for poor connections.

Scheme 399

Scheme 400

Control module monitors voltage on battery feed circuit. If control module detects that voltage is less than 8.6 volts for more than 4 seconds, force motor will shut off, TCC will be released, and transmission will shift to 2nd gear.

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

1. Normal system charging voltage is 10-17 volts.
2. This step checks whether generator, circuit 440 or PCM/TCM is the cause of Code 75.

Intermittents

Check for poor connections or damaged harness. Also, check for intermittent condition by starting engine and wiggling connection while monitoring battery voltage on "Scan" tool. If voltage status changes abruptly or engine stalls, check for loose connections.

Scheme 401

Scheme 402

The quad driver (inside PCM/TCM) has a fault detect circuit, which is monitored by PCM/TCM. PCM/TCM compares voltage values of fault detect circuit with acceptable values in PCM/TCM memory. If PCM/TCM senses voltage is not within acceptable range, Code 81 will be set.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks shift solenoid "B" and circuits inside transmission for shorts.
2. Battery voltage should be present at shift solenoid "B".
3. This step checks circuit 1223 for short to ground.
4. This step checks if PCM/TCM can control solenoid "B".
5. This determines whether circuit 1223 is open or PCM/TCM is faulty.

Check transmission pass-through connector and PCM/TCM for poor connections. Factory-installed PCM has an internal circuit breaker and should not need to be replaced.

Scheme 403

Scheme 404

The quad driver (inside PCM/TCM) has a fault detect circuit, which is monitored by PCM/TCM. PCM/TCM compares voltage values of fault detect circuit with acceptable values in PCM/TCM memory. If PCM/TCM senses voltage is not within acceptable range, Code 82 will be set.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks shift solenoid "A" and circuits inside transmission for shorts.
2. Battery voltage should be present at shift solenoid "A".
3. This step checks circuit 1222 for short to ground.
4. This step checks if PCM/TCM can control solenoid "A".

Check transmission pass-through connector and PCM/TCM for poor connections. Factory-installed PCM has an internal circuit breaker and should not need to be replaced.

Scheme 405

Scheme 406

The PCM/TCM quad driver has a fault detect circuit, which is monitored by PCM/TCM. PCM/TCM compares voltage values of fault detect circuit with acceptable values in PCM/TCM memory. If PCM/TCM senses voltage is not within acceptable range, Code 83 will be set.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks TCC solenoid and circuits inside transmission for shorts.
2. Battery voltage should be present at TCC solenoid.
3. This step checks circuit 422 for shorts to ground.
4. This step checks if PCM/TCM can control TCC solenoid.

Check transmission pass-through connector and PCM/TCM for poor connections. Factory-installed PCM has an internal circuit breaker and should not need to be replaced.

Scheme 407

Scheme 408

PCM/TCM compares input and output speed sensor values of transmission in each gear to acceptable values in PCM/TCM memory. If PCM/TCM senses sensor values are not within acceptable range, Code 85 will be set. This process takes place in all gears except Overdrive.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks operation of input sensor.
2. This step checks operation of output sensor.

Ensure pressure switch manifold is operating correctly. If illegal switch inputs are detected by PCM/TCM, Code 85 may be set. Check transmission pass-through connector and PCM/TCM for poor connections. "Scan" tool may be used to check gear ratios in each gear position. If gear ratio values are not correct, internal transmission problems may be present.

Scheme 409

Scheme 410

Code 86 will set under following conditions: vehicle speed is greater than 7 MPH, TPS value is more than 25% of total TPS travel, 1st or 2nd gear operation is requested by PCM/TCM, and transmission ratio indicates 3rd or 4th gear. All conditions must be met for 6 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks if PCM/TCM can control solenoid "B".

Check transmission pass-through connector. If problems are still present, check for possible internal transmission problems.

Scheme 411

Scheme 412

Code 87 will set under following conditions: vehicle speed is greater than 7 MPH, TPS value is more than 25% of total TPS travel, 3rd or 4th gear operation is requested by PCM/TCM, and transmission ratio indicates 1st or 2nd gear. All conditions must be met for 6 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks if PCM/TCM can control solenoid "B".
2. Battery supply should be present at PCM/TCM.
3. This step checks shift solenoid "B" and circuits inside transmission for shorts.

Check transmission pass-through connector. If problems are still present, check for possible internal transmission problems.

Scheme 413

ELECTRONIC TESTING

Note. If self-diagnostics are not used, following charts may help diagnose electronic transmission controls.

CLUTCH & BAND APPLICATION CHART

CLUTCH & BAND APPLICATION CHART

Scheme 414

The speed sensor, which is a Permanent Magnet (PM) generator, provides Digital Ratio Adapter Control (DRAC) with vehicle speed information. PM generator, mounted in transmission, produces a pulsing voltage signal whenever the vehicle speed is more than 3 MPH. Voltage level and pulse increase with vehicle speed. DRAC converts this signal to a pulsing signal by grounding circuit 437 (Brown wire) 2000 times per mile. Control module uses this signal in calculations to determine vehicle adjustments.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step tests for voltage variation while wheels are turning. Voltage will be low at low wheel speeds (4-6 volts at 20 MPH).
2. This step checks if vehicle speed sensor signal is present at DRAC.
3. This step checks output speed sensor signal.

Ensure all connectors are good. Very carefully check the pass-through connector at transmission. If input sensor is not working at start-up, output sensor will read zero.

Scheme 415

Scheme 416

The speed sensor, which is a Permanent Magnet (PM) generator, provides Digital Ratio Adapter Control (DRAC) with vehicle speed information. PM generator, mounted in transmission, produces a pulsing voltage signal whenever vehicle speed is more than 3 MPH. Voltage level and pulse increase with vehicle speed. DRAC converts this signal to a pulsing signal by grounding circuit 437 (Brown wire) 2000 times per mile. Control module uses this signal in calculations to determine vehicle adjustments.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step tests for voltage variation while wheels are turning. Voltage will be low at low wheel speeds (4-6 volts at 20 MPH).
2. This step checks if vehicle speed sensor signal is present at DRAC.
3. This step checks output speed sensor signal.

Ensure all connectors are good. Very carefully check the pass-through connector at transmission. If input sensor is not working at start-up, output sensor will read zero. If code 24 is set in computer memory, "Scan" tool will read engine RPM (input sensor signal).

Scheme 417

Scheme 418

The speed sensor, which is a Permanent Magnet (PM) generator, provides Digital Ratio Adapter Control (DRAC) with vehicle speed information. PM generator, mounted in transmission, produces a pulsing voltage signal whenever the vehicle speed is more than 3 MPH. Voltage level and pulse increase with vehicle speed. DRAC converts this signal to a pulsing signal by grounding circuit 437 (Brown wire) 2000 times per mile. Control module uses this signal in calculations to determine vehicle adjustments.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step tests for voltage variation while wheels are turning. Voltage will be low at low wheel speeds (4-6 volts at 20 MPH).
2. This step checks if vehicle speed sensor signal is present at DRAC.
3. This step checks vehicle speed sensor signal.

Using "Scan" tool, check for proper signal in Drive while wiggling wiring. Ensure all connectors are good. Very carefully check the pass-through connector at transmission. If input sensor is not working at start-up, output sensor will read zero. If Code 24 is set in computer memory, "Scan" tool will read engine RPM (input sensor signal).

Scheme 419

Scheme 420

The speed sensor, which is a Permanent Magnet (PM) generator, provides PCM/TCM with vehicle speed information. PM generator, mounted in transfer case, produces a pulsing voltage signal whenever vehicle speed is more than 3 MPH. Voltage level and pulse increase with vehicle speed. Control module uses this signal in calculations to determine vehicle adjustments.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step tests for voltage variation while wheels are turning. Voltage will be low at low wheel speeds (4-6 volts at 20 MPH).
2. This step checks output speed sensor signal.

Ensure all connectors are good. Very carefully check the pass-through connector at transmission. If input sensor is not working at start-up, output sensor will read zero.

Scheme 421

Scheme 422

The input speed sensor, which is a Permanent Magnet (PM) generator, provides PCM/TCM with engine (input) speed information. PM generator, mounted in transmission, produces a pulsing voltage signal whenever engine is running.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks input speed sensor circuit to PCM/TCM.
2. This step checks input speed sensor output.

Scheme 423

Scheme 424

When brake pedal is applied, switch opens circuit to PCM/TCM. If brake switch signal is incorrect, TCC operation may be affected.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks for voltage to brake switch.
2. This step checks if brake switch is open or faulty.
3. This step checks circuit 420 from brake switch to PCM/TCM.
4. This step simulates normal brake switch operation.

Check for problem with one or more of following components

1. Fuse, power supply circuit, brake switch or wire before splice
2. Wire or circuit problem between splice and PCM/TCM, poor connection to PCM/TCM or faulty PCM/TCM

Scheme 425

Scheme 426

TCC will engage under following conditions: vehicle speed is greater than 30 MPH, transmission is in 4th gear, engine and transmission are at normal operation temperatures, brake switch is closed, throttle position switch signal is steady, and no codes are stored.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step tests TCC solenoid and circuits inside transmission for shorts.
2. This step tests for power to transmission connector.
3. This step tests for short to ground in circuit 422.
4. This step tests for PCM/TCM control of TCC.

Check transmission pass-through connector and PCM/TCM for poor connections. TCC solenoid is pulse width modulated (frequency controlled) and will allow some slight slippage.

Scheme 427

Scheme 428

PCM/TCM turns on solenoid "A" during 1st and 4th gear operation. Solenoid "A" is off during 2nd and 3rd gear operation.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks shift solenoid "A" and circuits inside transmission for shorts.
2. Battery voltage should be present at shift solenoid "A".
3. This step checks circuit 1222 for short to ground.
4. This step checks if PCM/TCM can control solenoid "A".

Check transmission pass-through connector and PCM/TCM for poor connections. Factory-installed PCM has an internal circuit breaker and should not need to be replaced.

Scheme 429

Scheme 430

PCM/TCM turns on solenoid "B" during 3rd and 4th gear operation. Solenoid "B" is off during 1st and 2nd gear operation.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks shift solenoid "B" and circuits inside transmission for shorts.
2. Battery voltage should be present at shift solenoid "B".
3. This step checks circuit 1223 for short to ground.
4. This step checks if PCM/TCM can control solenoid "B".
5. This determines whether circuit 1223 is open or PCM/TCM is faulty.

Check transmission pass-through connector and PCM/TCM for poor connections. Factory-installed PCM has an internal circuit breaker and should not need to be replaced.

Scheme 431

Scheme 432

PCM/TCM monitors signal return amperage. If return amperage varies more than .16 amp from amperage sent by PCM/TCM, Code 73 will be set. If this occurs, force motor is disabled and maximum line pressure occurs.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks control of force motor by PCM/TCM.
2. Voltage should be present.
3. This step checks if problem is inside transmission.
4. This step checks for short to ground.
5. This step checks for high resistance inside transmission.

Check transmission pass-through connector and PCM/TCM for poor connections.

Scheme 433

Wiring Diagram ("C" & "K" Series - Gasoline Engine). Scheme 434

Wiring Diagram ("C" & "K" Series - Diesel Engine). Scheme 435

Wiring Diagram ("G" Series - Gasoline Engine). Scheme 436

Wiring Diagram ("G" Series - Diesel Engine). Scheme 437

Wiring Diagram ("R", "P" & "V" Series - Gasoline Engine). Scheme 438

Wiring Diagram ("R", "P" & "V" Series - Diesel Engine). Scheme 439

See also:
• AUTO TRANS DIAGNOSIS - GM TORQUE CONVERTER CLUTCH
• TESTS W/CODES - DIESEL
• TESTS W/CODES - TRANSMISSION
• TESTS W/CODES - V6
• TESTS W/CODES - V8
• CLUTCH & BAND APPLICATION CHART
• ELECTRONIC SELF-DIAGNOSTICS
• ELECTRONIC TESTING
• CLEARING TROUBLE CODES