Engine Controls - Tests W/codes - Transmission: Other GMC Pickup C3500

CODE 28, PRESSURE SWITCH MANIFOLD FAULT

The Pressure Switch Manifold (PSM) is actually 5 pressure switches combined into one unit and mounted on the transmission valve body. The PCM/TCM supplies battery voltage to the PSM on 3 separate wires. By grounding one or more of these circuits through various combinations of the pressure switches inside the pressure switch manifold, the PCM/TCM detects what gear range has been selected by the vehicle operator.

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

1. This test compares the indicated range to the range actually selected.
2. This test checks for correct voltage from the PCM/TCM to the transmission pass-thru connector.
3. This test will detect a short to ground in any one of the 3 PSM range circuits.

CODE 53, SYSTEM VOLTAGE HIGH

Code 53 will set when ignition is on and PCM terminal D1 voltage is greater than 19.5 volts for about 2 seconds. During the time the failure is present, the force motor is turned off, transmission immediately shifts to 2nd gear, and TCC operation is inhibited. The setting of additional codes may result.

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

1. Normal battery voltage is 10-17.0 volts.
2. This test checks if high voltage reading is due to the alternator, circuit No. 440 or PCM. With engine running, check voltage at battery. If voltage is greater than 19.5 volts, the PCM is okay.
3. This test checks if alternator is faulty under load condition. If voltage is greater than 19.5 volts, check alternator.

NOTES ON INTERMITTENTS

Jump-starting engine, and 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 207

Scheme 208

CODE 58, TRANSMISSION TEMP. SENSOR CKT (HIGH TEMP. INDICATED)

The transmission temperature sensor is a thermistor which controls the signal voltage to the PCM/TCM. The PCM/TCM applies and monitors voltage on circuit No. 1227 to the sensor. When transmission is cold, sensor resistance is high; therefore, the PCM/TCM will see high signal voltage. As the transmission warms up, sensor resistance and voltage will drop. At normal transmission operating temperature of 212°F (100°C), voltage will be about 1.5-2.0 volts.

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

1. Code 58 will set if signal voltage indicates a transmission temperature greater than 309°F (154°C) for one second.
2. This test determines if circuit No. 1227 is shorted to ground, which will result in conditions for Code 58.

CODE 59, TRANSMISSION TEMP. SENSOR CKT (LOW TEMP. INDICATED)

The transmission temperature sensor is a thermistor which controls signal voltage to PCM/TCM. The PCM/TCM applies and monitors 5 volts to the sensor on circuit No. 1227. When transmission is cold, sensor resistance is high; therefore, the PCM/TCM will see high signal voltage. As transmission temperature warms up, sensor resistance and voltage drop. At normal transmission operating temperature of 212°F (100°C), voltage will be about 1.5-2.0 volts.

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

1. Code 59 will set if signal voltage indicates a transmission temperature less than -54°F (-48°C) for one second.
2. This test simulates Code 58. If PCM/TCM recognizes the low signal voltage (high temperature) and scan tester reads 304°F (151°C) or greater, the PCM/TCM and wiring are okay.
3. This test determines if circuit No. 1227 is open. There should be 5 volts present at the sensor connector if measuring with a DVOM.

CODE 68, OVERDRIVE RATIO ERROR

The PCM/TCM monitors the difference in engine RPM and input shaft RPM. With transmission in Drive, scan tester reading should show engine speed closely matching input speed.

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

1. Code 68 will set under the following conditions: engine speed is 200 RPM greater than input speed, 4th gear is indicated, TCC is enabled, or if all conditions are met for 2 seconds.
2. This test monitors signal sent to the PCM/TCM from transmission.
3. This test confirms engine RPM signal to PCM/TCM.

CODE 73, FORCE MOTOR CURRENT (CURRENT ERROR)

Note. This flow chart requires the use of a bidirectional (Tech 1) scan tester.

The force motor is a PCM/TCM-controlled device used to regulate transmission line pressure. The PCM/TCM looks at TPS voltage, engine RPM and other inputs to determine appropriate line pressure for a given load, then regulates the pressure by applying a varying amperage. The applied amperage can vary from 1-1.1 amps.

The PCM/TCM then monitors amperage at the return line. If the return amperage varies more than .16 amp from the commanded amperage for the duration of at least one second, Code 73 will set. Once Code 73 is set, the force motor is disabled and full line pressure will be applied until the next time the ignition switch is cycled. Code 73 will remain stored, but the force motor will resume normal function until the conditions for Code 73 re-occur.

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

1. Checks the PCM and TCM's ability to command the force motor.
2. Checks for voltage at PCM/TCM.
3. Checks internal transmission harness and force motor for low resistance.
4. Checks for short to ground.
5. Checks internal transmission harness and force motor for high resistance.

CODE 75, SYSTEM VOLTAGE LOW

Code 75 will set when ignition is on and PCM terminal D1 voltage is less than 8.6 volts for about 4 seconds. During the time the failure is present, the force motor is turned off, maintaining only 2nd gear, and inhibiting 4th gear and TCC operation.

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

1. Normal battery voltage is 10-17.0 volts.
2. This test checks if the low voltage reading is due to the alternator, circuit No. 440 or PCM/TCM. With engine running, check voltage at the battery. If voltage is less than 8.6 volts, PCM/TCM is okay.

NOTE ON INTERMITTENTS

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. Minimum voltage allowed for Code 75 to set is on a graduated scale, and will change with temperature. Minimum voltage at -40°F (-40°C) is 6.7 volts. Minimum voltage at 304°F (150°C) is 10.5 volts, and minimum voltage at 194°F (90°C) is 8.6 volts.

Scheme 209

CODE 81, QDM FAULT (SOLENOID "B")

The PCM/TCM continually monitors voltage on each circuit connected to the quad driver, looking for either low or high voltage, depending on the commanded state of the devices connected to it. Code 81 will set if a fault has been detected on the shift solenoid "B" circuit. For example, if shift solenoid "B" is commanded on by the PCM/TCM, voltage on that circuit should drop when solenoid is grounded. If voltage stays up for at least .5 second, Code 81 will set. The opposite is also true. If shift solenoid "B" is off, voltage on the circuit should remain high. If voltage drops for more than .5 second, Code 81 will set.

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

1. This procedure checks shift solenoid "B" and internal transmission wiring for shorts.
2. This test checks for power, from the ignition through transmission fuse, to the shift solenoid "B".
3. This test ensures circuit No. 1223 is not shorted to ground.
4. This test checks PCM/TCM's ability to ground or control shift solenoid "B". If bidirectional scan tester is not available, solenoid may be activated by grounding ALDL test terminal "B" with ignition on and engine off.
5. This test ensures circuit No. 1223 is not shorted to ground.

CODE 82, QDM FAULT (SOLENOID "A")

The PCM/TCM continually monitors each circuit connected to the quad driver for either low or high voltage, depending on the commanded state of the device connected to it. Code 82 will set if there is a fault detected on the shift solenoid "A" circuit. For example, if shift solenoid "A" is commanded on by the PCM/TCM, then voltage on circuit should drop as soon as solenoid is grounded.

However, if voltage remains high for 2 seconds after the "on" command is given, Code 82 will set. The opposite is also true. If shift solenoid "A" is off, voltage on the circuit should be high. If voltage drops for .5 second or longer, Code 82 will set.

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

1. This procedure checks shift solenoid "A" and internal transmission wiring harness for shorts.
2. This test checks for power, from the ignition through the fuse, to the shift solenoid.
3. This test checks circuit No. 1222 for short to ground.
4. This test checks PCM/TCM's ability to ground or control shift solenoid "A". If bidirectional scan tester is not available, solenoid may be activated by grounding ALDL test terminal "B" with ignition on and engine off.

CODE 83, TCC QDM FAULT

The PCM/TCM continually monitors voltage on each circuit connected to the quad driver for either low or high voltage, depending on the commanded state of the device connected to it. Code 83 will set if PCM/TCM detects an inappropriate reading on the TCC circuit. For example, if the TCC duty cycle is zero, but voltage on the TCC circuit drops as if the solenoid were on, then Code 83 will set. The TCC solenoid, because of its large current draw, is connected to 2 terminals of a single quad driver.

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

1. This test checks for low resistance in the solenoid or internal transmission harness. This test also determines which circuit triggered the fault. If bidirectional scan tester is not available, TCC may be activated by grounding ALDL test terminal "B" with ignition on and engine off.

CODE 85, UNDEFINED RATIO

The PCM/TCM calculates the actual gear ratio from input and output speed readings while in each gear, then compares these to what the gear ratio should be, taking into consideration the selected gear range. This monitor includes Reverse gear, but does not include Overdrive gear.

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

1. This test verifies the proper function of the input sensor.
2. This test verifies the proper function of the output sensor.

CODE 86, SHIFT SOLENOID "B" STUCK "ON"

The shift solenoids are used inside the valve body to control spool valves, which determine the transmission gear. Fused ignition power is supplied to solenoid "B". The PCM/TCM will engage solenoid "B" by grounding circuit No. 1223 to energize the solenoid.

Code 86 will set under the following conditions.

1. Vehicle speed is greater than 7 MPH.
2. TPS is more than 25 percent.
3. PCM/TCM commands 1st or 2nd gear.
4. Transmission ratio indicates transmission is in 3rd or 4th gear.
5. Conditions are met for 6 seconds. NOTE: Test numbers refer to test numbers on diagnostic chart.

1. This test determines if transmission is receiving a solenoid "B" on command.

CODE 87, SHIFT SOLENOID "B" STUCK "OFF"

The shift solenoids are used inside the valve body to control spool valve position, which determines the transmission gear. Fused ignition power is supplied to solenoid "B." The PCM/TCM will engage solenoid "B" by grounding circuit No. 1223 to energize the solenoid.

Code 87 will set under the following conditions.

1. Vehicle speed is greater than 7 MPH.
2. TPS is more than 25 percent.
3. PCM/TCM commands 3rd or 4th gear.
4. Transmission ratio indicates transmission is in 1st or 2nd gear.
5. Conditions are met for 6 seconds. NOTE: Test numbers refer to test numbers on diagnostic chart.

1. This test checks PCM/TCM's ability to ground or control solenoid "B". If bidirectional scan tester is not available, solenoid may be activated by grounding ALDL test terminal "B" with ignition on and engine off.
2. This test checks the power supply and circuit No. 1223.
3. This test checks the internal transmission harness and solenoid "B".

OUTPUT SPEED SENSOR CIRCUIT CHECK (2WD) "C/K/G & P" SERIES

The output sensor circuit consists of a magnetic induction-type sensor, digital ratio adapter, and wiring. Gear teeth pressed on the outside diameter of the output carrier assembly induce an alternating current in the sensor.

This current is transmitted to a digital ratio adapter, where it is passed on to the PCM/TCM. The digital ratio adapter compensates for various axle ratios, and converts the signal to a square wave for use by the speedometer, cruise control and anti-lock brake system. If the input sensor is not operational at start up, it can cause the output sensor to read zero.

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

1. This test checks the speed signal on circuit No. 437 at the PCM/TCM from the digital ratio adapter.
2. This test checks for a speed signal from the output speed sensor to the digital ratio adapter.
3. This test checks the output speed sensor.

OUTPUT SPEED SENSOR CIRCUIT CHECK (4WD)

The output sensor is a magnetic induction type. Gear teeth pressed on the outside diameter of the output carrier assembly induce an alternating current in the sensor. Since vehicle speed is taken from the transfer case on 4WD drive vehicles, the transmission output sensor signal on these units goes directly to the PCM/TCM. If input sensor is not operational at start up, it can cause the output sensor to read zero.

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

1. This test checks for a speed signal at the PCM/TCM.
2. This test checks the output sensor directly.

INPUT SPEED SENSOR CIRCUIT CHECK

The input sensor is of the magnetic induction type and is located on the left side of the transmission, forward of center. Serrations in the forward clutch housing induce a small A/C current as they pass by the input sensor. While there is no specific code for an input sensor problem, the PCM/TCM uses input sensor readings to calculate gear ratio, turbine speed, TCC slip, and determine if the engine is running.

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

1. This test checks the input sensor circuit up to the PCM/TCM.
2. This test checks the sensor output.

BRAKE SIGNAL CIRCUIT CHECK

The normally closed brake switch supplies a 12-volt signal on circuit No. 420 to the PCM/TCM. The signal voltage is removed when brakes are applied. An incorrect brake signal may affect TCC operation.

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

1. This test checks for voltage at brake switch.
2. This test simulates closed brake switch (brakes off).
3. This test checks circuit No. 420 from brake switch to PCM/TCM.
4. This test opens circuit No. 420 and simulates condition of brakes being applied.

SHIFT SOLENOID "A" CIRCUIT CHECK

Shift solenoid "A" is attached to the valve body and is a normally open exhaust valve. The PCM/TCM activates the solenoid by grounding it through an internal quad driver. Solenoid "A" (Blue) is on in 1st and 4th gears, but is off in 2nd and 3rd gears. When solenoid is on, it redirects fluid to act on the shift valves.

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

1. This test checks shift solenoid "A" and the internal transmission wiring harness for shorts.
2. This test checks for power, from the ignition switch through the fuse, to the shift solenoid.
3. This test checks circuit No. 1222 for a short to ground.
4. This test checks PCM/TCM's ability to ground or control the shift solenoid "A". If bidirectional scan tester is not available, TCC may be activated by grounding ALDL test terminal "B" with ignition on and engine off.

SHIFT SOLENOID "B" CIRCUIT CHECK

The shift solenoids are used inside the valve body to control the spool valves, which determine the transmission gear. Fused ignition is supplied to solenoid "B". The PCM/TCM will engage solenoid "B" by grounding circuit No. 1223 to energize the solenoid.

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

1. This test checks shift solenoid "B" and the internal transmission wiring for shorts.
2. This test checks for power, from the ignition through the transmission fuse, to the shift solenoid "B".
3. This test checks PCM/TCM's ability to ground or control the shift solenoid "B".
4. This test ensures circuit No. 1223 is not shorted to ground.
5. This test checks PCM/TCM's ability to ground or control the shift solenoid "B". If bidirectional scan tester is not available, TCC may be activated by grounding ALDL test terminal "B" with ignition on and engine off.
6. This test ensures circuit No. 1223 is not shorted to ground.

FORCE MOTOR CIRCUIT CHECK

Note. This flow chart requires the use of a bidirectional (Tech 1) scan tester.

The force motor is a PCM/TCM-controlled device used to regulate transmission line pressure. The PCM/TCM looks at TPS voltage, engine RPM, and other inputs to determine the appropriate line pressure for a given load, then regulates the pressure by applying a variable amperage to the force motor. The applied amperage varies from .1-1.1 amps.

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

1. Checks the PCM and TCM's ability to command the force motor.
2. Checks for voltage at PCM/TCM.
3. Checks internal transmission harness and force motor for low resistance.
4. Checks for short to ground.
5. Checks internal transmission harness and force motor for high resistance.