Engine Controls - Tests W/codes - Transmission: Diagnosis GMC Vandura P3500

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, refer to the following articles in this section

1. «THEORY/OPERATION»(ref-10257) And
2. «TESTS W/CODES - GASOLINE»(ref-10255)

Diesel vehicles 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 in this article. 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. See DIAGNOSTIC CIRCUIT CHECK in «BASIC TESTING»(ref-10260) article in this section. This determines if the 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»(ref-10262) article in this section.

ENTERING & EXITING DIAGNOSTIC MODE

1. With key on and engine off, connect a jumper wire between ALDL terminal "B" (diagnostic terminal) and terminal "A" (ground). (Scheme 136) This places the control unit into diagnostic mode.
2. In this mode, the control unit will display Code 12 by flashing the SERVICE ENGINE SOON (SES) light. Code 12 is identified by the 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 the diagnostic terminal is ungrounded. To exit diagnostic mode, turn ignition off and remove jumper wire from ALDL connector.

Scheme 136

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, remove PCM/TCM memory battery voltage 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 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 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/TCM detects one of 2 "illegal" PSM combinations. See VALID PSM COMBINATION table for various combinations. Check pass-thru connector for good contact.

VALID PSM COMBINATION

Code 28 Schematic - Pressure Switch Manifold Fault. Scheme 137

Code 28 Flow Chart - Pressure Switch Manifold Fault. Scheme 138

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.

Code 39 Schematic - Converter Clutch Stuck "OFF" Position. Scheme 139

Code 39 Flow Chart - Converter Clutch Stuck "OFF" Position. Scheme 140

Check harness routing for a potential short to ground in circuit No. 1227. Scan tester displays transmission 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 RESISTANCE table. An out-of-calibration sensor could result in delayed shifts, or TCC enabled complaint.

TRANSMISSION SENSOR RESISTANCE

Code 58 Schematic - Transmission Temp. Sensor Circuit High Temperature Indicated. Scheme 141

Code 58 Flow Chart - Transmission Temp. Sensor Circuit High Temperature Indicated. Scheme 142

Scan tester displays transmission temperature in degrees Centigrade. After transmission is running, the displayed temperature should rise steadily to about 212°F (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 coolant sensor at various temperature levels to determine if sensor is out of calibration. See the TRANSMISSION SENSOR RESISTANCE table. An out-of-calibration sensor could result in firm shifts, or TCC enabled complaint.

Code 59 Flow Chart - Transmission Temp. Sensor Circuit Low Temperature Indicated. Scheme 143

Check for spread connectors at pass-thru connector. Code 68 will set when going to default (2nd gear). Refer to TESTS W/O CODES article in this section.

Code 68 Schematic - Overdrive Ratio Error. Scheme 144

Code 68 Flow Chart - Overdrive Ratio Error. Scheme 145

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

Code 73 Schematic - Force Motor Current (Current Error). Scheme 146

Code 73 Flow Chart - Force Motor Current (Current Error). Scheme 147

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

Code 81 Schematic - QDM Fault (Solenoid "B"). Scheme 148

Code 81 Flow Chart - QDM Fault (Solenoid "B"). Scheme 149

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

Code 82 Schematic - QDM Fault (Solenoid "A"). Scheme 150

Code 82 Flow Chart - QDM Fault (Solenoid "A"). Scheme 151

Ensure to 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.

Code 83 Flow Chart - TCC QDM Fault. Scheme 152

The PCM/TCM relies on the Pressure Switch Manifold (PSM) to indicate what gear range has been selected. PSM 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.

GEAR RATIO

Code 85 Schematic - Undefined Ratio. Scheme 153

Code 85 Flow Chart - Undefined Ratio. Scheme 154

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

Code 86 Schematic - Shift Solenoid "B" Stuck "ON". Scheme 155

Code 86 Flow Chart - Shift Solenoid "B" Stuck "ON". Scheme 156

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

Code 87 Flow Chart - Shift Solenoid "B" Stuck "OFF". Scheme 157

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.

Output Speed Sensor Ckt. Schematic (2WD Except "C" & "K"). Scheme 158

Output Speed Sensor Ckt. Flow Chart (2WD Except "C" & "K"). Scheme 159

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

Output Speed Sensor Ckt. Schematic (2WD "C" & "K" Series). Scheme 160

Output Speed Sensor Ckt. Flow Chart (2WD "C" & "K" Series). Scheme 161

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

Output Speed Sensor Ckt. Schematic (4WD Vehicles). Scheme 162

Output Speed Sensor Ckt. Flow Chart (4WD Vehicles). Scheme 163

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

Input Speed Sensor Ckt. Check Schematic. Scheme 164

Input Speed Sensor Ckt. Check Flow Chart. Scheme 165

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).

Brake Signal Circuit Check Schematic (All Engines). Scheme 166

Brake Signal Circuit Check Flow Chart (All Engines). Scheme 167

Check all connections, especially those at the transmission pass-thru connector. If code is intermittent, see INTERMITTENTS in the 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.

Torque Converter Clutch (TCC) Ckt. Check Flow Chart. Scheme 168

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

Shift Solenoid "A" Ckt. Check Flow Chart. Scheme 169

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

Shift Solenoid "B" Circuit Check Flow Chart. Scheme 170

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

Force Motor Circuit Check Flow Chart. Scheme 171