Engine Controls - Tests W/codes - Transmission: Other Chevrolet Pickup C1500

CODE 37, BRAKE SWITCH STUCK ON

The normally closed brake switch supplies a 12-volt signal on circuit No. 420 to the PCM. The signal voltage is removed when brakes are applied. An incorrect brake signal may affect TCC and 4th gear operation in hot mode.

Code 37 will set when circuit No. 420 is open, vehicle speed less than 5 MPH for 6 seconds, then between 5 MPH and 20 MPH for 6 seconds, then greater than 20 MPH for 6 seconds, for a complete total of 7 times.

Note. Test numbers refer to numbers on diagnostic chart. Display may vary depending upon manufacturer of scan tester. Display may read APPLIED, RELEASED, ON or OFF.

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.
4. This test opens circuit No. 420 and simulates brakes being applied.

CODE 38, BRAKE SWITCH STUCK OFF

The normally closed brake switch supplies a 12-volt signal on circuit No. 420 to the PCM. The signal voltage is removed when brakes are applied. An incorrect brake signal may affect TCC and 4th gear operation.

Code 38 will set when circuit No. 420 has voltage, vehicle speed is greater than 20 MPH for 6 seconds, then between 5 MPH and 20 MPH for 6 seconds, for a complete total of 7 times.

Note. Test numbers refer to numbers on diagnostic chart. Display may vary depending upon manufacturer of scan tester. Display may read APPLIED, RELEASED, ON or OFF.

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.
4. This test opens circuit No. 420 and simulates brakes being applied.

CODE 52, LONG SYSTEM VOLTAGE HIGH

Code 52 will set when ignition is on and PCM battery feed terminal voltage is greater than 16 volts for 109 minutes. During the time the failure is present, the pressure control solenoid is turned off, transmission immediately shifts to 3rd gear, and TCC operation is inhibited. The setting of additional diagnostic trouble codes may result.

Note. Test numbers refer to numbers on diagnostic chart.

1. Normal battery voltage is 9-15 volts.
2. This test checks if high voltage reading is due to alternator, circuit No. 440 or PCM. With engine running, check voltage at battery. If voltage is greater than 15 volts, PCM is okay.
3. This test checks if alternator is faulty under load condition. If voltage is greater than 15 volts, check alternator.

CODE 53, SYSTEM VOLTAGE HIGH

Code 53 will set when ignition is on and PCM battery feed terminal voltage is greater than 19.5 volts for 2 seconds. During the time the failure is present, the pressure control solenoid is turned off, transmission immediately shifts to 3rd gear, and TCC operation is inhibited. The setting of additional diagnostic trouble codes may result.

Note. Test numbers refer to numbers on diagnostic chart.

1. Normal battery voltage is 9-15 volts.
2. This test checks if the high voltage reading is due to alternator, circuit No. 440 or PCM. With engine running, check voltage at battery. If voltage is greater than 15 volts, PCM is okay.
3. This test checks if alternator is faulty under load condition. If voltage is greater than 15 volts, check alternator.

CODE 66, 3-2 CONTROL SOLENOID CIRCUIT FAULT

The 3-2 control solenoid hydraulically coordinates the apply rate of the 2-4 band with hydraulic release of the 3-4 clutch during a 3-2 downshift. 3-2 circuit duty cycle is continually monitored by the PCM depending on the command state of the circuit. When the transmission is in 1st gear the duty cycle of the solenoid is equal to zero. When the transmission is in 2nd gear or higher, the duty cycle of the solenoid will be about 90 percent. When the transmission downshifts 3-2, the duty cycle of the solenoid will be about 20 percent.

For example, if the PCM commands the solenoid on, the duty cycle on that circuit should drop when the solenoid is grounded. If voltage stays up for 4 seconds, Code 66 will set. If the 3-2 control solenoid is off, the duty cycle on the circuit should remain high. If voltage drops for 4 seconds, Code 66 will set. When code is set, a soft landing to 3rd gear will occur.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks 3-2 control solenoid and internal transmission harness for short circuits.
2. This test checks for power, from the ignition through the fuse, to the 3-2 control solenoid.
3. This test ensures circuit No. 897 is not shorted to ground.
4. This test checks ability of PCM to ground or control 3-2 control solenoid. If bidirectional scan tester is not available, solenoid may be activated by grounding ALDL test terminal "B" with ignition on and engine off.

CODE 67, TCC SOLENOID CIRCUIT CHECK

The TCC solenoid is a normally open exhaust valve. The PCM will engage the solenoid by grounding circuit No. 422 with an internal quad-driver. The PCM continually monitors voltage on TCC circuit for either low or high voltage, depending on the commanded state of the circuit. Code 67 will set if a fault is detected.

For example, If the PCM commands the TCC solenoid on, the voltage on that circuit should drop when the solenoid is grounded. If voltage stays up for 2 seconds, Code 67 will set. If solenoid is off, the voltage on that circuit should remain higher. If voltage drops for 2 seconds, Code 67 will set. When code is set, no TCC will occur and no 4th gear in hot mode.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks TCC solenoid and the internal transmission harness for short circuits.
2. This test checks for power, from the ignition through the fuse, to the TCC solenoid.
3. This test ensures circuit No. 422 is not shorted to ground.
4. This test checks ability of PCM to ground or control TCC solenoid.

2WD & AWD

The Vehicle Speed Sensor (VSS) circuit consists of a magnetic induction-type sensor, vehicle speed sensor buffer module 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 the buffer module. The buffer module compensates for various axle ratios, and converts the signal to a square wave for use by the speedometer, cruise control, anti-lock brake system and PCM.

The buffer module sends 2 different signals to the PCM. Circuit No. 437 relays the transmission output speed which is used to control shift points, line pressure, TCC, Code 24 and Code 72. Circuit No. 1716 relays the vehicle speed which is used to control engine operating functions and Code 16.

Code 72 will set under the following conditions.

1. When in gear other than Park/Neutral, transmission output speed changes greater than 1000 RPM.
2. When in Park/Neutral, transmission output speed changes greater than 2050 RPM.
3. Conditions are met for 2 seconds.

4WD

The Vehicle Speed Sensor (VSS) circuit consists of a magnetic induction-type sensor, vehicle speed sensor buffer module, 4WD low switch 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 the buffer module. The buffer module compensates for various axle ratios, and converts the signal to a square wave for use by the speedometer, cruise control, anti-lock brake system and PCM.

The buffer module sends 2 different signals to the PCM. Circuit No. 437 relays the transfer case output speed to the PCM. PCM uses both the transfer case output speed signal and the 4WD low switch to determine transmission output shaft speed. PCM uses transmission output shaft speed to control shift points, line pressure, TCC, Code 24 and Code 72. Circuit No. 1716 relays the vehicle speed which is used to control engine operating functions and Code 16.

Code 72 will set under the following conditions.

1. When in gear other than Park/Neutral, transmission output speed changes greater than 1000 RPM.
2. When in Park/Neutral, transmission output speed changes greater than 2050 RPM.
3. Conditions are met for 2 seconds. NOTE: Test numbers refer to numbers on diagnostic chart.

1. This test checks the VSS signal to the PCM.
2. This test checks the VSS signal to the buffer module.
3. This test checks the VSS signal.

CODE 73, PRESSURE CONTROL SOLENOID (CURRENT ERROR)

The pressure control solenoid is a PCM-controlled device used to regulate transmission line pressure. The PCM 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 pressure control solenoid. Applied amperage varies from .1 to 1.1 amps.

The PCM then monitors the amperage at the return line. If the return amperage varies greater than .16 amp from the commanded amperage for at least one second, Code 73 will set. When Code 73 sets, the full line pressure will be applied, causing harsh shifts until the next ignition cycle. The code will remain stored in memory, and the pressure control solenoid will resume normal operation until conditions for the code reoccur.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks ability of PCM to command pressure control solenoid.
2. This test checks for voltage at PCM.
3. This test checks internal transmission harness and pressure control solenoid for low resistance.
4. This test checks internal transmission harness and pressure control solenoid for high resistance.

CODE 75, SYSTEM VOLTAGE LOW

Code 75 will set when ignition is on and PCM terminal E16 voltage is less than temperature to voltage scale for about 4 seconds. During the time the failure is present, the pressure control solenoid is turned off, maintaining only 3rd gear, and inhibiting TCC operation.

Minimum voltage allowed for Code 75 to set is on a graduated scale and changes with temperature. Minimum voltage at -40°F (-40°C) is 7.3 volts. Minimum voltage at 302°F (150°C) is 11.7 volts, and minimum voltage at 194°F (90°C) is 10.3 volts.

Note. Test numbers refer to numbers on diagnostic chart.

1. Normal battery voltage is 9-15 volts.
2. This test checks if low voltage reading is due to alternator, circuit No. 440 or PCM. With engine running, check voltage at the battery. If voltage is less than 8.6 volts, PCM is okay.

CODE 81, 2-3 SHIFT SOLENOID CIRCUIT FAULT

The PCM 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 2-3 shift solenoid circuit.

If 2-3 shift solenoid is commanded on by the PCM, voltage on that circuit should drop when solenoid is grounded. If 2-3 shift solenoid is off, voltage on the circuit should remain high. If solenoid is shorted off, 3rd gear only will occur. If solenoid is shorted on, 2nd gear only will occur. If voltage stays up for at least 2 seconds, Code 81 will set. If voltage drops for more than 2 seconds, Code 81 will set.

Note. Test numbers refer to numbers on diagnostic chart.

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

CODE 82, 1-2 SHIFT SOLENOID CIRCUIT FAULT

The PCM 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 82 will set if a fault has been detected on the 1-2 shift solenoid circuit.

If 1-2 shift solenoid is commanded on by the PCM, voltage on that circuit should drop when solenoid is grounded. If Code 82 sets, the transmission will allow 2nd and 3rd gears only, or 1st and 4th gears only. If voltage stays up for at least 2 seconds after 1-2 shift solenoid is commanded on, Code 82 will set. If 1-2 shift solenoid is off, voltage on the circuit should be high. If voltage drops for more than 2 seconds, Code 82 will set.

Note. Test numbers refer to numbers on diagnostic chart.

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

VEHICLE SPEED SENSOR CHECK (2WD & AWD)

The Vehicle Speed Sensor (VSS) circuit consists of a magnetic induction-type sensor, vehicle speed sensor buffer module and wiring. Gear teeth, pressed on the outside diameter of output carrier assembly, induce an alternating current in the sensor. This current is transmitted to the buffer module. Buffer module compensates for various axle ratios, and converts signal to a square wave for use by speedometer, cruise control, anti-lock brake system and PCM. 5 Buffer module sends 2 different signals to PCM. Circuit No. 437 relays transmission output speed, which is used to control shift points, line pressure, TCC, Code 24 and Code 72. Circuit No. 1716 relays vehicle speed, which is used to control engine operating functions and Code 16.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks the VSS signal to the PCM.
2. This test checks the VSS signal to the buffer module.
3. This test checks the VSS signal.

VEHICLE SPEED SENSOR CHECK (4WD)

The Vehicle Speed Sensor (VSS) circuit consists of a magnetic induction-type sensor, vehicle speed sensor buffer module, 4WD low switch and wiring. Gear teeth, pressed on outside diameter of output carrier assembly, induce an alternating current in the sensor. This current is transmitted to the buffer module. Buffer module compensates for various axle ratios, and converts signal to a square wave for use by speedometer, cruise control, anti-lock brake system and PCM.

Buffer module sends 2 different signals to PCM. Circuit No. 437 relays transfer case output speed to PCM. PCM uses transfer case output speed signal and 4WD low switch to determine transmission output shaft speed. PCM uses transmission output shaft speed to control shift points, line pressure, TCC, Code 24 and Code 72. Circuit No. 1716 relays vehicle speed, which is used to control engine operating functions and Code 16.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks VSS signal to PCM.
2. This test checks VSS signal to the buffer module.
3. This test checks VSS signal.

BRAKE SIGNAL CIRCUIT CHECK

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

Note. Test numbers refer to numbers on diagnostic chart. Display may vary depending upon manufacturer of scan tester. Display may read APPLIED, RELEASED, ON or OFF.

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.
4. This test opens circuit No. 420 and simulates condition of brakes being applied.

3-2 CONTROL SOLENOID CIRCUIT CHECK

The 3-2 control solenoid hydraulically coordinates the apply rate of the 2-4 band with hydraulic release of the 3-4 clutch during a 3-2 downshift. The 3-2 circuit duty cycle is continually monitored by PCM depending on command state of circuit. When transmission is in 1st gear, duty cycle of solenoid is equal to zero. When transmission is in 2nd gear or higher, duty cycle of solenoid will be about 90 percent. When transmission downshifts 3-2, duty cycle of solenoid will be about 20 percent.

For example, if PCM commands solenoid on, duty cycle on that circuit should drop when solenoid is grounded. If voltage stays up for 4 seconds, a code will set. If 3-2 control solenoid is off, duty cycle on circuit should remain high. If voltage drops for 4 seconds, a code will set. When code is set, a soft landing to 3rd gear will occur.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test check 3-2 control solenoid and internal transmission harness for short circuits.
2. This test checks for power, from the ignition through the fuse, to the 3-2 control solenoid.
3. This test ensures circuit No. 897 is not shorted to ground.
4. This test checks ability of PCM to ground or control 3-2 control solenoid. If bidirectional scan tester is not available, solenoid may be activated by grounding ALDL test terminal "B" with ignition on and engine off.

1-2 SHIFT SOLENOID CIRCUIT CHECK

The 1-2 shift solenoid is attached to valve body and is a normally open exhaust valve. PCM engages solenoid by grounding circuit No. 1222 with an internal quad-driver. The 1-2 shift solenoid is on in 1st and 4th gears, and off in 2nd and 3rd gears. When on, 1-2 shift solenoid redirects fluid to act on shift valves.

Note. Test numbers refer to numbers on diagnostic chart.

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

2-3 SHIFT SOLENOID CIRCUIT CHECK

Shift solenoids are used inside valve body to control spool valves and determine transmission gear. The 2-3 shift solenoid is on in 1st and 2nd gears, and off in 3rd and 4th gears. Fused battery ignition voltage is supplied to 2-3 shift solenoid. PCM engages solenoid by grounding circuit No. 1223.

Note. Test numbers refer to numbers on diagnostic chart.

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

PRESSURE CONTROL SOLENOID CIRCUIT CHECK

Pressure control solenoid is a PCM-controlled device used to regulate transmission line pressure. PCM looks at TPS voltage, engine RPM, and other inputs to determine appropriate line pressure for a given load, then regulates pressure by applying a variable amperage to pressure control solenoid. Applied amperage varies from .1 to 1.1 amps.

PCM then monitors amperage at return line. If return amperage varies greater than .16 amp from commanded amperage for at least one second, Code 73 will set. When Code 73 sets, full line pressure will be applied, causing harsh shifts until next ignition cycle. Code will remain stored in memory, and pressure control solenoid will resume normal operation until conditions for code reoccur.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks ability of PCM to command pressure control solenoid.
2. This test checks for voltage at PCM.
3. This test checks internal transmission harness and pressure control solenoid for low resistance.
4. This test checks internal transmission harness and pressure control solenoid for high resistance.

CODE 28, PRESSURE SWITCH MANIFOLD FAULT

The Pressure Switch Manifold (PSM), also referred to as fluid pressure switch assembly, 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 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 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 will set when ignition is on and PCM/TCM 12-volt battery feed 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 numbers on diagnostic chart.

1. Normal battery voltage is 9-15 volts.
2. This test checks if high voltage reading is due to the alternator, circuit No. 440 or PCM/TCM. With engine running, check voltage at battery. If voltage is greater than 15 volts, the PCM/TCM is okay.
3. This test checks if alternator is faulty under load condition. If voltage is greater than 15 volts, check alternator.

NOTES ON INTERMITTENTS

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 211

Scheme 212

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 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, and 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, also referred to as pressure control solenoid, 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 to 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 numbers on diagnostic chart.

1. Checks the ability of the PCM/TCM 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 will set when ignition is on and PCM/TCM 12-volt battery feed voltage is less than 8.6 volts for about 4 seconds. During the time failure is present, force motor, also referred to as pressure control solenoid, is turned off, maintaining only 2nd gear, and inhibiting TCC operation.

Note. Test numbers refer to numbers on diagnostic chart.

1. Normal battery voltage is 9-15 volts.
2. This test checks if low voltage reading is due to alternator, circuit No. 440 or PCM/TCM. With engine running, check voltage at 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 changes 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 213

CODE 81, SOLENOID "B" CIRCUIT FAULT

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, also referred to as 2-3 shift solenoid. 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 2 seconds, 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 2 seconds, Code 81 will set.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks shift solenoid "B" and internal transmission wiring for short circuits.
2. This test checks for power, from the ignition through the fuse, to the shift solenoid.
3. This test ensures circuit No. 1223 is not shorted to ground.
4. This test checks ability of PCM/TCM 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, SOLENOID "A" CIRCUIT FAULT

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, also referred to as 1-2 shift solenoid. 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 numbers on diagnostic chart.

1. This test checks shift solenoid "A" and internal transmission wiring harness for short circuits.
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 ability of PCM/TCM 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 SOLENOID CIRCUIT 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 numbers on diagnostic chart.

1. This test checks for low resistance in the solenoid or internal transmission harness. Test also determines which circuit triggered fault. If bidirectional scan tester is not available, TCC may be activated by grounding ALDL test terminal "B" with ignition on and engine off.
2. This test checks for voltage in the solenoid.
3. This test checks circuit No. 422 for short to ground.
4. This test checks if PCM/TCM is commanding TCC solenoid on.

CODE 85, UNDEFINED GEAR RATIO

While in each gear, PCM/TCM calculates actual gear ratio from input and output speed readings, also referred to as vehicle speed, then compares these to what gear ratio should be, taking into consideration selected gear range. This monitor includes reverse gear, but does not include overdrive gear.

Scheme 214

Note. Test numbers refer to 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 (vehicle speed sensor).

CODE 86, LOW GEAR RATIO

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", also referred to as 2-3 shift solenoid. PCM/TCM engages solenoid "B" by grounding circuit No. 1223.

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 numbers on diagnostic chart.

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

CODE 87, HIGH GEAR RATIO

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", also referred to as 2-3 shift solenoid. PCM/TCM engages solenoid "B" by grounding circuit No. 1223.

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 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".

VEHICLE SPEED SENSOR CHECK

The Vehicle Speed Sensor (VSS) circuit consists of a magnetic induction-type sensor, VSS buffer module (also referred to as the DRAC) and wiring. Gear teeth, pressed on outside diameter of output carrier assembly, induce an alternating current in sensor. This current is transmitted to the buffer module, where it is passed on to the PCM/TCM. The buffer module 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.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks the VSS signal to the PCM/TCM.
2. This test checks the VSS signal to the buffer module.
3. This test checks the VSS signal.

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 and TCC slip, and determine if engine is running.

Note. Test numbers refer to numbers on diagnostic chart.

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

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 numbers on diagnostic chart. Display may vary depending upon manufacturer of scan tester. Display may read APPLIED, RELEASED, ON or OFF.

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.

PRESSURE SWITCH MANIFOLD CIRCUIT CHECK

A fault in the Pressure Switch Manifold (PSM) circuit, also referred to as fluid pressure switch assembly circuit, should result in the setting of a related trouble code. If a problem is suspected with this circuit and a code is not set, go to CODE 28, PRESSURE SWITCH MANIFOLD FAULT chart under TROUBLE CODE CHARTS (4L80-E) for diagnosis.

SHIFT SOLENOID "A" CIRCUIT CHECK

Shift solenoid "A", also referred to as 1-2 shift solenoid, 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" (Gray) 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 numbers on diagnostic chart.

1. This test checks shift solenoid "A" and the internal transmission wiring harness for short circuits.
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

Shift solenoid "B", also referred to as 2-3 shift solenoid, is attached to the valve body and is a normally open exhaust valve, which determine the transmission gear. Solenoid "B" (Green) is on in 3rd and 4th gears, but is off in 1st and 2nd gears. Fused ignition is supplied to solenoid "B". PCM/TCM engages solenoid "B" by grounding circuit No. 1223.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks shift solenoid "B" and the internal transmission wiring for short circuits.
2. This test checks for power, from the ignition through the fuse, to the shift solenoid.
3. This test ensures circuit No. 1223 is not shorted to ground.
4. This test checks ability of PCM/TCM 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.
5. 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, also referred to as pressure control solenoid, is a PCM/TCM-controlled device used to regulate transmission line pressure. PCM/TCM looks at TPS voltage, engine RPM, and other inputs to determine appropriate line pressure for a given load, then regulates pressure by applying a variable amperage to the force motor. Applied amperage varies from .1 to 1.1 amps.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks the ability of the PCM/TCM 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.