Engine Controls - Tests W/codes - Transmission: Diagnosis Chevrolet Pickup K1500

SELF-DIAGNOSTIC SYSTEM

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, see THEORY/OPERATION and appropriate TESTS W/CODES article in this sections.

Diesel vehicles with 4L80-E transmission are equipped with a Transmission Control Module (TCM). TCM controls only the electronic transmission. Unless specifically stated otherwise, references to PCM also apply to TCM-equipped vehicles.

Control module is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, control module will illuminate the SERVICE ENGINE SOON light located on instrument panel. 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. On gasoline vehicles, see DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section. On diesel vehicles, DIAGNOSTIC CIRCUIT CHECK is covered in G - DIESEL TESTS W/ CODES article in this section. The diagnostic circuit 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 SERVICE ENGINE SOON light to come on.
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 SERVICE ENGINE SOON light will go out 10 seconds after fault goes away. For intermittent diagnosis procedures, see TESTS W/O CODES article in this section.

ENTERING & EXITING DIAGNOSTIC MODE

Note. The Assembly Line Data Link (ALDL) may also be referred to as the Data Link Connector (DLC) in flow charts.

1. With key on and engine off, connect a jumper wire between ALDL terminal "B" (test terminal) and terminal "A" (ground). (Scheme 152) This places control module into diagnostic mode.
2. In this mode, control module will display Code 12 by flashing SERVICE ENGINE SOON (SES) light. Code 12 is identified by SES light flashing 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 test terminal is ungrounded. To exit diagnostic mode, turn ignition off and remove jumper wire from ALDL connector.

Scheme 152

CLEARING TROUBLE CODES

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 TESTS W/O CODES article in this section for intermittent diagnostic procedures.

SPECIAL TOOLS (DIAGNOSTIC)

Special scan testers are plugged into the ALDL to read trouble codes and check system voltages on serial data line. These testers can save a great deal of time. For additional information, see 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 ALDL test terminal "B" with ignition on and engine off.

Diagnostic Aids

Code 28 will set if PCM detects one of 2 "illegal" fluid pressure switch assembly combinations. See VALID FLUID PRESSURE SWITCH ASSEMBLY COMBINATION table below for various combinations. Check pass-thru connector for good contact.

VALID FLUID PRESSURE SWITCH ASSEMBLY COMBINATION

Scheme 153

Scheme 154

Scheme 155

If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section. Check customer driving habits and/or unusual traffic conditions (i.e., stop-and-go expressway traffic).

Scheme 156

Scheme 157

If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section. Check customer driving habits and/or unusual traffic conditions (i.e., stop-and-go expressway traffic).

Circuit No. 440 supplies battery voltage to the PCM. Jump-starting engine or charging battery with a battery charger may set Code 53. If code is set when an accessory is operated, check for poor connections or excessive current draw. Also check for poor connections at starter solenoid or fusible link.

Scheme 158

Scheme 159

Scheme 160

Circuit No. 440 supplies battery voltage to the PCM. Jump-starting engine or charging battery with a battery charger may set Code 53. If code is set when an accessory is operated, check for poor connections or excessive current draw. Also check for poor connections at starter solenoid or fusible link.

Check harness routing for a potential short to ground in circuit No. 1227. 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. See TRANSMISSION SENSOR - TEMP TO RESISTANCE chart. An out-of-calibration sensor could result in delayed shifts, or TCC enabled complaint. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Scheme 161

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. A faulty connection or an open in circuit No. 455 or circuit No. 1227 will result in a Code 59. Test the transmission sensor at various temperature levels to determine if sensor is out of calibration. See TRANSMISSION SENSOR - TEMP TO RESISTANCE chart. An out-of-calibration sensor could result in firm shifts, or TCC enabled complaint.

Scheme 162

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

Scheme 163

Scheme 164

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

Scheme 165

Scheme 166

Check for stall with parking brake applied and in 2nd gear. Check all connections, especially those at the transmission pass-thru connector. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section. Some slight TCC slippage is normal. If Code 69 is set and Code 67 is not set, problem could be internal to the transmission.

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

Scheme 167

Scheme 168

Scheme 169

Check all connections, especially those at the transmission pass-thru connector and PCM.

Scheme 170

Scheme 171

Circuit No. 440 supplies battery voltage to PCM. If code sets when an accessory is operated, check for poor connections or excessive current draw. Also, check for poor connections at starter solenoid or fusible link.

Scheme 172

Check harness routing for a potential short to ground in circuit No. 1227. 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. See TRANSMISSION SENSOR - TEMP TO RESISTANCE chart. An out-of-calibration sensor could result in delayed shifts or TCC enabled complaint. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Check all connections, especially those at the transmission pass-thru connector. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section. An open in the circuit can cause multiple codes to set.

Scheme 173

Scheme 174

SHIFT SOLENOID COMBINATION

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

Scheme 175

Scheme 176

SHIFT SOLENOID COMBINATION

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

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

If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section. Check customer driving habits and/or unusual traffic conditions (i.e., stop-and-go expressway traffic).

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

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

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

SHIFT SOLENOID COMBINATION

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

SHIFT SOLENOID COMBINATION

Check all connections, especially those at the transmission pass-thru connector and PCM.

Code 28 will set if PCM detects one of 2 "illegal" fluid pressure switch assembly combinations. See VALID FLUID PRESSURE SWITCH ASSEMBLY COMBINATION table below for various combinations. Check pass-thru connector for good contact.

VALID FLUID PRESSURE SWITCH ASSEMBLY COMBINATION

Code 28 will set if PCM/TCM detects one of 2 "illegal" PSM combinations. See VALID PSM COMBINATION table for various combinations. Check pass-thru connector for good contact.

Scheme 177

Scheme 178

VALID PSM COMBINATION

Clear codes and re-check for Code 39. If code resets, problem could be internal to the transmission. Code 39 will only set in 3rd gear. TCC slip in 4th gear will set Code 68.

Scheme 179

Scheme 180

Scheme 181

Check harness routing for a potential short to ground in circuit No. 1227. 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. See TRANSMISSION SENSOR - TEMP TO RESISTANCE chart. An out-of-calibration sensor could result in delayed shifts or TCC enabled complaint.

Scheme 182

Scheme 183

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 circuit No. 455/452 or circuit No. 1227 will result in a Code 59. Test the transmission sensor at various temperature levels to determine if sensor is out of calibration. See TRANSMISSION SENSOR - TEMP TO RESISTANCE chart. An out-of-calibration sensor could result in firm shifts or TCC enabled complaint. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Scheme 184

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 TESTS W/O CODES article in this section.

Scheme 185

Scheme 186

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

Scheme 187

Scheme 188

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

Scheme 189

Scheme 190

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

Scheme 191

Scheme 192

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

Scheme 193

Scheme 194

Scheme 195

The PCM/TCM relies on Vehicle Speed Sensor Buffer Module (DRAC) to indicate what gear range has been selected. DRAC must be functioning properly or Code 85 may be set. Check all connections, especially those at the transmission pass-thru connector. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section. Compare scan tester gear ratio reading to specifications in GEAR RATIO table.

Scheme 196

GEAR RATIO

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

Scheme 197

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

Scheme 198

Check all connections, especially at transmission pass-thru connector. If the input sensor is not operational at start up, it can cause the VSS to read zero. While Code 24 is set, scan tester will display RPM derived from input speed.

Scheme 199

Scheme 200

Scheme 201

Scheme 202

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

Scheme 203

Scheme 204

If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section. Check customer driving habits and/or unusual traffic conditions (i.e., stop-and-go expressway traffic).

Scheme 205

Scheme 206

Check all connections, especially those at the transmission pass-thru connector. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section. The TCC solenoid is pulse width modulated, and is designed to keep the TCC right at the point of engagement. Therefore, some slight slippage is normal.

Scheme 207

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

Scheme 208

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

Scheme 209

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

Scheme 210