Engine Controls - Tests W/codes - Electronic Transmission: Diagnosis Chevrolet Pickup C3500

DIAGNOSTIC INFORMATION

Note. SERVICE ENGINE SOON light, located on instrument cluster, is also referred to as the Malfunction Indicator Light (MIL).

Gasoline vehicles are equipped with a Powertrain Control Module (PCM). The PCM controls engine/emission functions, and electronic-controlled transmission functions. For additional information on self-diagnostic system for gasoline vehicles, proceed to THEORY/OPERATION - GASOLINE article and appropriate G - GASOLINE TESTS W/ CODES articles in this section.

1. «TESTS W/CODES - 4.3L»(ref-19732)
2. «TESTS W/CODES - 5.0L»(ref-19750)
3. «TESTS W/CODES - 5.7L»(ref-19751)
4. «TESTS W/CODES - 7.4L»(ref-19752)

Control module is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, control module will illuminate the Malfunction Indicator Light (MIL) located on instrument cluster. When malfunction is detected and light is turned on, a corresponding trouble code will be stored in control module memory. To retrieve stored codes, see ENTERING & EXITING DIAGNOSTIC MODE . Malfunctions are recorded as either hard failures or intermittent failures.

Preliminary Inspection

1. Check all vacuum hoses for correct routing, restrictions, cuts or other damage. Inspect difficult-to-see vacuum hoses beneath the air cleaner assembly and other engine components.
2. Inspect all engine compartment wiring for proper connections. Also check wires for pinched or chaffed spots, as well as contact with sharp edges or exhaust manifolds.
3. The preliminary inspection is very important and should be performed carefully and thoroughly, as it can often lead to fixing a problem without further diagnosis.

Diagnostic Procedure

1. Ensure all non-controlled systems not related to engine or transmission control system are operating properly. DO NOT proceed with testing unless all other non-controlled system problems are repaired.
2. ALWAYS begin system diagnosis with checking diagnostic circuit or system. On gasoline vehicles, see DIAGNOSTIC CIRCUIT CHECK in «BASIC TESTING - GASOLINE»(ref-19753) article in this section. On diesel vehicles, DIAGNOSTIC SYSTEM CHECK is covered in «TESTS W/CODES - 6.5L DIESEL»(ref-19760) article in this section. The diagnostic circuit or system check determines if computer-controlled system is working properly. If trouble codes are displayed (other than Code 12), determine if codes are hard or intermittent trouble codes.
3. A hard code is one which is present while working on vehicle, and problem still exists. Hard codes will cause the Malfunction Indicator Light (MIL) to come on. NOTE: SERVICE ENGINE SOON light, located on instrument cluster, is also referred to as the Malfunction Indicator Light (MIL).
4. An intermittent code is one which does not reset itself and is NOT present while working on vehicle. Intermittent codes are often caused by loose connections. The MIL will go out 10 seconds after fault goes away. For intermittent diagnosis procedures, see appropriate TESTS W/O CODES article in this section. See below. «TESTS W/O CODES - GASOLINE»(ref-19726) «TESTS W/O CODES - 6.5L DIESEL»(ref-19762)

ENTERING & EXITING DIAGNOSTIC MODE

1. With ignition on and engine off, connect a jumper wire between Data Link Connector (DLC) terminal "B" (diagnostic terminal) and terminal "A" (ground). (Scheme 423) This places control module into diagnostic mode.
2. In this mode, PCM will display Code 12 by flashing the MIL once, followed by a short pause, then 2 flashes in quick succession.
3. Code 12 will be displayed 3 times. If no other codes are stored, Code 12 will continue to flash until diagnostic terminal is ungrounded. To exit diagnostic mode, turn ignition off and remove jumper from DLC.

Scheme 423

CLEARING TROUBLE CODES

Note. To prevent PCM/TCM damage, ensure ignition switch is in OFF position when disconnecting or reconnecting power to PCM/TCM.

Trouble codes should be cleared after repairs have been completed. Also, some diagnostic charts require that codes be cleared before using diagnostic chart. To clear codes, disconnect PCM/TCM power feed for 30 seconds.

If no hard fault codes are present (only intermittent codes exist), proceed to appropriate TESTS W/O CODES article in this section. See below for intermittent diagnostic procedures.

1. «TESTS W/O CODES - GASOLINE»(ref-19726)
2. «TESTS W/O CODES - 6.5L DIESEL»(ref-19762)

SPECIAL TOOLS (DIAGNOSTIC)

Special scan testers, plugged into the DLC, may be used to read trouble codes, and check voltages in system on serial data line. These testers can save a great deal of time. For additional information, see owner's manual included with tester.

TEST EQUIPMENT

A tachometer, test light, Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, vacuum gauge, and jumper wires are required to test and diagnose electronic transmission control system. A scan tester may also be used to access data parameters. Tester will supply a visual reading of most inputs, and some outputs, to the PCM/TCM. Some diagnostic flow charts require the use of a bidirectional (Tech 1) scan tester.

TROUBLE CODE CHARTS

The following diagnostic flow charts and circuit schematics are provided courtesy of General Motors Corp.

Note. Some charts require the use of a bidirectional (Tech 1) scan tester. If a bidirectional scan tester is not available, the PCM/TCM-controlled relays and solenoids may be energized by grounding DLC diagnostic terminal "B" with ignition on and engine off.

Diagnostic Aids

Code 24 will set when no vehicle speed is detected at vehicle start off. Code 72 will set when VSS signal is present and is lost. Check all connections, especially those at transmission pass-through connector. If code is intermittent, proceed to INTERMITTENTS in the TESTS W/O CODES - 6.5L DIESEL article in this section. While Code 24 is set, scan tester will display an RPM derived from input speed. If input speed sensor is not operational at start-up, this can cause VSS to read zero.

Code 24 Schematic ("C", "K", "G" & "P" Series). Scheme 424

Code 24 Flow Chart. Scheme 425

Code will set if PCM detects one of 2 illegal combinations. Check all connections for good contact. An intermittent may be caused by a poor connection, chaffed wire insulation or a broken wire. Monitor voltage of each terminal while moving related harness connectors. If failure is induced, voltage reading will change.

VALID PSM COMBINATION (4L60-E)

VALID PSM COMBINATION (4L80-E)

Code 28 Schematic (4L60-E Transmission (Diesel) Transmission Range Pressure Switch. Scheme 426

Code 28 Schematic (4L60-E Transmission (Gasoline) Transmission Range Pressure Switch. Scheme 427

Code 28 Schematic (4L80-E Transmission (Diesel) Transmission Range Pressure Switch. Scheme 428

Code 28 Schematic (4L80-E Transmission (Gasoline) Transmission Range Pressure Switch. Scheme 429

Code 28 Flow Chart Transmission Range Pressure Switch. Scheme 430

If code is intermittent, check customer driving habits (driving with foot resting on brake pedal) or for unusual traffic conditions (stop and go expressway traffic).

Codes 37/38 Schematic ("C" & "K" Series) TCC Brake Switch On/Off. Scheme 431

Codes Flow Chart TCC Brake Switch On/Off. Scheme 432

If TCC is mechanically stuck on, vehicle speed is zero MPH, brakes are applied and D2 is selected, the TCC fluid will mechanically apply the TCC causing an engine stall.

Code 39 Schematic (Diesel) TCC Stuck Off. Scheme 433

Code 39 Schematic (Gasoline) TCC Stuck Off. Scheme 434

Code 39 Flow Chart TCC Stuck Off. Scheme 435

Check harness routing for a potential short to ground in TFT signal circuit. Scan tester displays transmission fluid temperature in degrees Centigrade. After transmission is running, the temperature display should rise steadily to about 100°C then stabilize. Test the transmission sensor at various temperature levels to determine if sensor is out of calibration. An out-of-calibration sensor could result in delayed shifts or TCC enabled complaint.

Code 58 Schematic (4L80-E Gasoline) Transmission Fluid Temperature High. Scheme 436

Code 58 Flow Chart Transmission Fluid Temperature High. Scheme 437

Scan tester displays transmission fluid temperature in degrees Centigrade. After transmission is running, the displayed temperature should rise steadily to about 100°C then stabilize. A faulty connection or an open in ground circuit or signal circuit will result in a Code 59. Test the transmission sensor at various temperature levels to determine if sensor is out of calibration. An out-of-calibration sensor could result in firm shifts or TCC enabled complaint. If code is intermittent, see INTERMITTENTS in appropriate TESTS W/O CODES article in this section. See below.

1. «TESTS W/O CODES - GASOLINE»(ref-19726)
2. «TESTS W/O CODES - 6.5L DIESEL»(ref-19762)

Code 59 Flow Chart Transmission Fluid Temperature Low. Scheme 438

Check all connections, especially those at the transmission pass-thru connector. If code is intermittent, see INTERMITTENTS in appropriate TESTS W/O CODES article in this section. See below. Some slight TCC slippage is normal. 3-2 control solenoid feedback normally oscillates on/off when the duty cycle is applied.

1. «TESTS W/O CODES - GASOLINE»(ref-19726)
2. «TESTS W/O CODES - 6.5L DIESEL»(ref-19762)

Code 66 Schematic Control Solenoid Circuit Fault. Scheme 439

Code 66 Flow Chart. Scheme 440

Check all connections, especially those at the transmission pass-thru connector. If code is intermittent, see INTERMITTENTS in appropriate TESTS W/O CODES article in this section. See below. Some slight TCC slippage is normal.

1. «TESTS W/O CODES - GASOLINE»(ref-19726)
2. «TESTS W/O CODES - 6.5L DIESEL»(ref-19762)

Code 67 Schematic (4L60-E Diesel) TCC Solenoid Circuit Check. Scheme 441

Code 67 Schematic (4L60-E Gasoline) TCC Solenoid Circuit Check. Scheme 442

Code 67 Flow Chart TCC Solenoid Circuit Check. Scheme 443

Check for spread connectors at pass-thru connector. Code 68 will set when going to default (2nd gear). If code is intermittent, see INTERMITTENTS in appropriate TESTS W/O CODES article in this section. See below.

1. «TESTS W/O CODES - GASOLINE»(ref-19726)
2. «TESTS W/O CODES - 6.5L DIESEL»(ref-19762)

Code 68 Flow Chart Overdrive Ratio Error. Scheme 444

If the TCC is mechanically stuck on, TCC fluid will apply the TCC causing an engine stall.

Code 69 Schematic (4L60-E Diesel) Torque Converter Clutch Stuck On. Scheme 445

Code 69 Schematic (4L80-E Gasoline) Torque Converter Clutch Stuck On. Scheme 446

Code 69 Flow Chart Torque Converter Clutch Stuck On. Scheme 447

Code 72 will set when VSS signal is present and is lost. Code 24 will set when no vehicle speed is detected at vehicle start off. Check all connections, especially those at transmission pass-through connector. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES - 6.5L DIESEL article in this section.

Code 72 Schematic ("C" & "K" Series Diesel) VSS Circuit Loss Transmission Output Signal. Scheme 448

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

Code 73 Schematic (Diesel) Pressure Control Solenoid (Current Error). Scheme 449

Code 73 Schematic (Gasoline) Pressure Control Solenoid (Current Error). Scheme 450

Code 73 Flow Chart Pressure Control Solenoid (Current Error). Scheme 451

Check for poor connections in PCM/TCM related circuits.

Code 74 Schematic (Diesel) Transmission Input Speed Error. Scheme 452

Code 74 Schematic (Gasoline) Transmission Input Speed Error. Scheme 453

Code 74 Schematic Flow Chart Transmission Input Speed Error. Scheme 454

Check harness routing for a potential short to ground in signal circuit. Scan tester displays transmission fluid temperature in degrees Centigrade. After transmission is running, the temperature display should rise steadily to about 100°C then stabilize. Test the transmission sensor at various temperature levels to determine if sensor is out of calibration. An out-of-calibration sensor could result in delayed shifts or TCC enabled complaint.

Code 79 Flow Chart Transmission Fluid Temperature High. Scheme 455

Check all connections, especially those at transmission pass-thru connector. If code is intermittent, see INTERMITTENTS in appropriate TESTS W/O CODES article in this section. See below.

1. «TESTS W/O CODES - GASOLINE»(ref-19726)
2. «TESTS W/O CODES - 6.5L DIESEL»(ref-19762)

Code 81 Schematic (Diesel) Transmission 2-3 Error. Scheme 456

Code 81 Schematic (Gasoline) Transmission 2-3 Error. Scheme 457

Code 81 Flow Chart Transmission 2-3 Error. Scheme 458

Check all connections, especially at the transmission pass-thru connector. If code is intermittent, see INTERMITTENTS in appropriate TESTS W/O CODES article in this section. See below.

1. «TESTS W/O CODES - GASOLINE»(ref-19726)
2. «TESTS W/O CODES - 6.5L DIESEL»(ref-19762)

Code 82 Schematic (Diesel) Transmission 1-2 Error. Scheme 459

Code 82 Schematic (Gasoline) Transmission 1-2 Error. Scheme 460

Code 82 Flow Chart Transmission 1-2 Error. Scheme 461

Check all connections, especially those at the transmission pass-thru connector. If code is intermittent, see INTERMITTENTS in appropriate TESTS W/O CODES article in this section.

1. «TESTS W/O CODES - GASOLINE»(ref-19726)
2. «TESTS W/O CODES - 6.5L DIESEL»(ref-19762)

Code 83 Schematic (Diesel) TCC Solenoid Circuit Fault. Scheme 462

Code 83 Schematic (Gasoline) TCC Solenoid Circuit Fault. Scheme 463

Code 83 Flow Chart TCC Solenoid Circuit Fault. Scheme 464

Code will set when an unknown gear ratio is detected for any gear but 4th. Check all connections, especially those at the transmission pass-thru connector. If code is intermittent, see INTERMITTENTS in appropriate TESTS W/O CODES article in this section. See below. Compare scan tester gear ratio reading to specifications in GEAR RATIO SPECIFICATIONS .

1. «TESTS W/O CODES - GASOLINE»(ref-19726)
2. «TESTS W/O CODES - 6.5L DIESEL»(ref-19762)

GEAR RATIO SPECIFICATIONS

Code 85 Schematic (4L80-E Diesel) Undefined Gear Ratio. Scheme 465

Code 85 Schematic (4L80-E Gasoline) Undefined Gear Ratio. Scheme 466

Code 85 Flow Chart (4L80-E Gasoline) Undefined Gear Ratio. Scheme 467

If code is intermittent, see INTERMITTENTS in appropriate TESTS W/O CODES article in this section.

1. «TESTS W/O CODES - GASOLINE»(ref-19726)
2. «TESTS W/O CODES - 6.5L DIESEL»(ref-19762)

Code 86 Flow Chart (4L60-E Gasoline) Low Gear Ratio Error. Scheme 468

Check all connections, especially those at the transmission pass-thru connector. Fault may be an internal transmission problem.

Code 87 Flow Chart (4L60-E Gasoline) High Gear Ratio Error. Scheme 469