Diagnosis - 4L60-E: Other Chevrolet Pickup K3500

TRANSMISSION CONTROLS

Shift solenoid holds hydraulic pressure when it is on and releases pressure when it is off. This action controls the shift valves inside valve body. By switching one or both solenoids on or off, different combinations of clutches, sprags and bands are operated. See CLUTCH & BAND APPLICATION under TROUBLE SHOOTING.

PCM

The PCM is located under air cleaner on Brougham, Caprice and Roadmaster; at right rear corner of engine compartment on Camaro and Firebird, and above power brake booster on Corvette. The PCM is located behind glove box on all light duty truck vehicles except "G" Series. On "G" Series, PCM is under driver's seat.

PCM controls TCC, pressure control solenoid (hydraulic pressure) and shifting solenoids 1-2 and 2-3. In addition, PCM also controls ignition, fuel and emission devices related to the engine.

The PCM receives electronic signals from sensors and switches. These signals help the PCM determine when to operate various relays and solenoids related to engine and transmission components.

SENSORS & SWITCHES

The PCM controls converter clutch lock-up, upshifts and downshifts based on transmission temperature, system voltage, throttle position, transmission oil pressure switches (5), and transmission output and input (engine) speed sensors. (Scheme 233) The system includes several other switches and sensors that are used for engine control (gasoline engines). For additional information and testing of engine components, see appropriate article in ENGINE PERFORMANCE section.

Shift Solenoids 1-2 & 2-3

Transmission is shifted up or down by 2 electric solenoids. Both solenoids are located on valve body. (Scheme 233) Ignition power is supplied to each solenoid by the transmission fuse. Solenoid 1-2 controls hydraulic pressure to 1-2 shift valves. Solenoid 2-3 controls hydraulic pressure to 2-3 shift valve.

Note. The 3-4 shift is directly controlled by the hydraulic circuits in valve body.

Pressure Control

Pressure control (duty-cycle motor) solenoid has a spool valve and operates pressure regulator valve. (Scheme 233) The computer sends a frequency signal to the pressure control solenoid to regulate hydraulic line pressure. The frequency signal (duty cycle) is measured with a dwell meter or lab scope. When the duty cycle is zero, line pressure is at maximum, and pressure control solenoid draws zero amp. When the duty cycle is 60%, line pressure is at minimum, and pressure control solenoid draws 1.1 amps at 4-5 volts.

TCC Solenoid

This solenoid is used to control TCC apply valve. The computer sends a frequency signal to the TCC solenoid to gradually apply or release the TCC. (Scheme 233)

3-2 Control Solenoid

PCM modulates current (duty cycle) to control 3-2 control solenoid. The 3-2 control solenoid is off in first gear. In all other gears, 3-2 control solenoid is 90 percent on. Hydraulic pressure is regulated to smoothly release the 3-4 clutch and 2-4 apply band during 3-2 downshift.

Scheme 233

Incorrect Shift Pattern

Check TP sensor, VSS, shift solenoids, 4WD low switch (light trucks and vans only) or performance switch (Camaro and Firebird with V8 only).

Shift Quality

Check TP sensor, VSS, transmission temperature sensor, engine coolant temperature sensor, shift solenoids, pressure switch assembly, pressure control solenoid or manual and/or performance switches (Camaro and Firebird with V8 only).

Engine Rough

Check TP sensor.

Line Pressure Too High

Check pressure switch assembly, system voltage or pressure control solenoid.

Line Pressure Too Low

Check pressure control solenoid.

MIL Stuck On

Check engine speed (tachometer) sensor.

Erratic Manual Downshift

Check pressure switch assembly.

Unwanted Downshift (Corvette Only)

Check Acceleration Slip Regulation (ASR) system.

Wrong Gear, No Shift Or Two Gears Only

Check shift solenoids.

Second Gear Start (Camaro & Firebird With V6 Engine Only)

Check second gear start switch.

3rd Gear Only

Check system voltage or 3-2 control solenoid.

Delayed 3-4 Upshift & TCC Apply During Hard Acceleration

Check cruise control.

No 4th Gear Hot

Check engine speed (tachometer) sensor, pressure switch assembly, brake switch, system voltage or TCC solenoid.

No TCC Apply

Check engine speed (tachometer) sensor, pressure switch assembly, brake switch, system voltage, or TCC solenoid.

TCC Apply Time Wrong

Check VSS, transmission temperature sensor.

RETRIEVING CODES (WITH SCAN TESTER)

Note. To read trouble codes and check system voltages on serial data line, plug scan tester into ALDL.

The scan tester is a specialized tester which, when plugged into ALDL, can be used to diagnose on-board computer control systems by providing instant access to circuit voltage information without need to crawl under dash or hood to backprobe sensors and connectors.

Scan testers may also furnish information on status of output devices (solenoids and relays). However, status parameters are only an indication that output signals have been sent to devices by the control module. It does not indicate if devices have responded properly to that signal. This will need to be checked at output device using a voltmeter or test light.

Note. Code 12 should always exist when ALDL is grounded with key on and engine off, but may not be indicated by all makes of Scan testers.

If trouble code is not present, this is not an indication there is no problem. Driveability-related problems with codes displayed occur about 20 percent of the time, while driveability problems without codes occur about 80 percent of the time.

Out-of-specification sensors WILL NOT set trouble code, but WILL cause driveability problems. Using scan tester is the easiest method of checking sensor specifications and other data parameters. Intermittent wiring problems may be identified by wiggling wiring harnesses and connections (key on, engine off) while observing scan tester.

Note. If erroneous voltage signals are suspected, it will be necessary to verify tester information using digital voltmeter and wiring schematic. If non-existent codes are displayed, turn ignition off, remove tester, turn ignition on, and ground ALDL test terminal "B". The same codes should be retrieved whether scan tester or TRANS or SERVICE ENGINE SOON light is used.

Intermittent Simulation

To reproduce the conditions causing intermittent fault, use the following methods

1. Lightly vibrate component.
2. Heat component.
3. Wiggle or bend wiring harness.
4. Spray component with water.
5. Remove/apply vacuum source.

Monitor circuit/component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.

Possible Cause & Correction

To track down possible causes of an intermittent SERVICE ENGINE SOON light, check the following items

1. Check for poor mating of one connector to another. Terminals may not be fully seated. Check for improperly formed or damaged terminals. Check wire to terminal connections.
2. Check wire from SERVICE ENGINE SOON light to PCM for short to ground.
3. Check wire from test terminal "B" of ALDL for intermittent short to ground.
4. Check for poor connections in PCM ground terminals.
5. Check for loss of trouble code memory. To check code memory on fuel injected models, disconnect TP sensor and run engine at idle until SERVICE ENGINE SOON light comes on. Code 22 (or appropriate TP sensor code) should be stored and retained in memory when ignition is turned off. If code is not stored, PCM is faulty.
6. Check for electrical system interference caused by a defective relay, or an PCM-driven solenoid or switch which may cause sharp electrical surge. This type of problem will normally occur when faulty component is operated.
7. Check for aftermarket parts which may not have been produced to manufacturer's specifications. Solenoids without original-equipment diodes for circuit protection, and HEI-EST module or voltage regulator using transistors instead of silicon-chip circuitry may possibly cause voltage surges (up to 300 volts) in PCM wiring, causing temporary PCM shutdown. PCM shutdown is a normal response to system overvoltage (greater than 16-17 volts on most models). PCM will repower when condition no longer exists. This could cause a flickering SERVICE ENGINE SOON light and stumble, with no codes set in memory.
8. Check for any open diodes in A/C or engine wiring.
9. Check for improper installation of electrical accessories such as auxiliary lights or 2-way radios.
10. Ensure EST (gas engine) wires are kept away from spark plug wires, distributor wires, distributor housing, ignition coil and generator. Ensure ground wire from PCM to distributor or ignition module is connected to a good ground.

CHART A-1 (CAMARO & FIREBIRD W/4.3L)

1. If engine starts, go to step 3). If engine does not start, check for blown fuses in PCM ignition and PCM battery feed circuits. Check and repair circuits if blown fuses are present.
2. If fuses are okay, turn ignition off. Disconnect PCM connector and turn ignition on. Check for battery and ignition voltage at appropriate PCM connector terminals. If voltage is not present, repair open circuit. If voltage is present, check for faulty PCM grounds, faulty connections at PCM or faulty PCM.
3. If engine started in step 1), disconnect PCM connectors. Using a jumper wire, connect terminal B7 (Brown/White wire) of PCM connector to ground. If test light stays off, repair open circuit, burned bulb, or Brown/White wire shorted to voltage as necessary. If test light is on, PCM connector is faulty or PCM is faulty.

CHART A-1 (BROUGHAM, CAPRICE, CAMARO, CORVETTE, FIREBIRD & ROADMASTER W/5.7L)

1. If engine starts, go to step 3). If engine does not start, check for blown fuses in PCM ignition and PCM battery feed circuits. Check and repair circuits if blown fuses are present.
2. If fuses are okay, turn ignition off. Disconnect PCM connector and turn ignition on. Check for battery and ignition voltage at appropriate PCM connector terminals. If voltage is not present, repair open circuit. If voltage is present, check for faulty PCM grounds, faulty connections at PCM or faulty PCM.
3. If engine started in step 1), connect Scan tester to ALDL connector. If Scan tester can display serial data, go to CODE DTC-11. If Scan tester cannot display serial data, turn ignition off.
4. Disconnect PCM connector and turn ignition on. Check for ignition voltage at PCM connector terminal D3 (Pink or Pink/Black wires). If voltage is not present, repair open ignition circuit. If voltage is present, check for faulty PCM grounds, faulty connections at PCM or faulty PCM.

CHART A-2 (BROUGHAM, CAPRICE, CAMARO, CORVETTE, FIREBIRD & ROADMASTER W/5.7L)

1. If MIL lamp does not flash with engine at idle, go to step 3). If MIL lamp flashes with engine at idle, turn ignition off. Disconnect PCM connector "D" ("C" on Corvette).
2. Connect one end of test light to battery positive terminal. Touch other end to terminal "B" of the ALDL connector. If test light is on, repair circuit shorted to ground. If test light stays off, PCM is faulty.
3. If MIL lamp did not flash in step 1), check for 5 volts at terminal "B" of the ALDL connector. If 5 volts are present, repair faulty connector at PCM or replace PCM. If 5 volts are not present, turn ignition off.
4. Disconnect PCM connector "D" ("C" on Corvette). Using a jumper wire, connect terminal "B" of ALDL connector to ground. Connect one end of test light to battery positive terminal. Touch other end to appropriate PCM terminal of the "D" connector ("C" on Corvette). If test light stays off, repair open circuit. If test light is on, PCM connector is faulty or PCM is faulty.

CHART A-1 - ("C", "G", "K", "L", "M", "S" & "T" W/GAS ENGINE)

1. If engine starts, go to step 3). If engine does not start, check for blown fuses in PCM ignition and PCM battery feed circuits. Check and repair circuits if blown fuses are present.
2. If fuses are okay, turn ignition off. Disconnect PCM connector and turn ignition on. Check for battery and ignition voltage at appropriate PCM connector terminals. If voltage is not present, repair open circuit. If voltage is present, check for faulty PCM grounds, faulty connections at PCM or faulty PCM.
3. If engine started in step 1), turn ignition off. Disconnect PCM connector and turn ignition on. Using a test light, ground circuit at MIL control terminal of PCM connector (Brown/White wire). If MIL lamp does not go on, check MIL bulb, check related circuits and repair as necessary. If MIL lamp goes on, check for faulty PCM grounds, faulty connections at PCM or faulty PCM.

CHART A-2 ("C", "G", "K", "L", "M", "S" & "T" W/GAS ENGINE)

1. Turn ignition on, but leave engine off. If MIL lamp is off, go to CHART A-1. If MIL lamp is on, ground diagnostic connector. If MIL lamp does not flash code DTC-12, go to next step. If MIL lamp flashes code DTC-12, check serial data circuit for shorts or opens. If circuit is okay, PCM or PROM may be faulty.
2. If MIL lamp is off from step 1), turn ignition off. Disconnect PCM connectors. Turn ignition on. If MIL lamp goes on, check for short in circuit from MIL bulb to PCM connector.
3. If MIL lamp stays off, turn ignition off. Reconnect PCM connectors. Turn ignition on, but leave engine off. Make sure diagnostic connector is not grounded. Using a test light, back probe diagnostic connector terminal "B" at PCM (Black/White or White/Black wire).
4. If MIL lamp does not flash DTC-12, go to next step. If MIL lamp flashes DTC-12, check circuit (Black/White or White/Black wire) between diagnostic connector terminal "B" and PCM connector for short to ground.
5. If MIL lamp does not flash DTC-12 from step 4), check PROM installation. If PROM is installed correctly, replace PCM using original PROM. If code DTC-12 is now present, system is okay. If code DTC-12 is still not present, replace PROM.

Scheme 234

Scheme 235

MIL should be on when engine if off and ignition is on. Switched battery voltage is supplied to MIL. The ECM turns light on by providing a ground path through circuit No. 419.

Note. Test numbers refer to numbers on diagnostic chart.

1. If fusible link is blown, see WIRING DIAGRAMS article for complete circuit.
2. Using a test light connected to 12 volts, probe each of the system ground circuits to ensure a good ground is present. See PIN VOLTAGE CHARTS article.

CODE 22, THROTTLE POSITION SENSOR SIGNAL VOLTAGE LOW

CODE 22 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if code is result of a hard failure or an intermittent condition.
2. This test simulates conditions for Code 21. If control module recognizes change of state, control module and wiring are okay.
3. This simulates a high signal voltage to check for an open in TPS signal line to control module. Scan tester should recognize this signal and display high TPS voltage.

CODE 58, TRANS. TEMPERATURE SENSOR HIGH TEMPERATURE - 3.4L "F" BODY, 4.3L & 5.7L

PCM supplies and monitors a 5-volt reference to sensor. As transmission temperature changes, sensor resistance changes, affecting monitored voltage. When fluid is cold, resistance is high, resulting in a high monitored voltage. When fluid is hot, resistance is low, resulting in a low monitored voltage.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for a short to ground or an out-of-calibration sensor.
2. Checks for an internal fault within the transmission by creating an open.

CODE 59, TRANS. TEMPERATURE SENSOR LOW TEMPERATURE - 3.4L "F" BODY, 4.3L & 5.7L "B", "D", "F" & "Y" BODIES

PCM supplies and monitors a 5-volt reference to sensor. As transmission temperature changes, sensor resistance changes, affecting monitored voltage. When fluid is cold, resistance is high, resulting in a high monitored voltage. When fluid is hot, resistance is low, resulting in a low monitored voltage.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for an out-of-calibration sensor.
2. Simulates a Code 58. If PCM recognizes low signal voltage, and scan displays 146 degrees centigrade or higher, PCM and wiring are okay.
3. Checks if signal circuit is open. Five volts should be present at sensor connector.

CODE 72, VEHICLE SPEED SENSOR LOSS - 3.4L "F" BODY, 4.3L & 5.7L "B", "D" & "F" BODIES

Speed sensor is a PM generator located on transmission output shaft.

Note. Test numbers refer to numbers on diagnostic chart.

1. Disable Traction Control (TC) system (if equipped) when performing this step. Whenever ignition is cycled off and then back on, TC system will default on.
2. An intermittent connection at VSS or PCM may cause code to set. Inspect harness and all related connections. Check for damage or pushed out terminals.
3. Ensure harness is not routed too close to hot exhaust components.

CODE 72, VEHICLE SPEED SENSOR LOSS - 5.7L "Y" BODY

Speed sensor is a PM generator located on transmission output shaft.

Note. Test numbers refer to numbers on diagnostic chart.

1. Disable Traction Control (TC) system (if equipped) when performing this step. Whenever ignition is cycled to off position and then back to on, TC system will default on.

CODE 75, TRANSMISSION VOLTAGE LOW - 4.3L & 5.7L

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for normal battery voltage of 9-15 volts.
2. Checks if low voltage is due to generator voltage supply circuit, or PCM. If voltage is less than 9 volts, PCM is okay.

CODE 85, TCC STUCK ON - 4.3L & 5.7L

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks mechanical state of TCC when PCM commands TCC solenoid off. TCC slip speed should increase.

CODE 96, TRANSMISSION VOLTAGE LOW - 3.4L "F" BODY

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for normal battery voltage of 9-15 volts.
2. Checks if low voltage is due to generator voltage supply circuit, or PCM. If voltage is less than 9 volts, PCM is okay.

CODE 97, VSS OUTPUT CIRCUIT - 4.3L & 5.7L

Note. Test numbers refer to numbers on diagnostic chart.

1. Disable Traction Control (TC) system (if equipped) prior to this step. Switch is located in glove box. Whenever ignition is cycled off and then on, TC system will default to on. If vehicle speed is indicated at this point, code is intermittent.
2. Use Jumper Harness (J 35616-A) to prevent damage to harness.

CODE 16, TRANSMISSION OUTPUT SPEED - 5.0L & 5.7L WITH 4L60E TRANSMISSION

VSS signal buffer supplies 2002 pulses per mile to PCM on vehicle speed signal circuit. Code 16 will set if this signal is lost due to an open or grounded signal line.

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

1. This tests for battery voltage at VSS buffer.
2. This tests for proper ground path for VSS buffer.
3. This tests for VSS buffer signal to PCM.
4. This test checks for faulty connections and a faulty VSS buffer.

CODE 21, TPS SIGNAL VOLTAGE HIGH

Throttle Position Sensor (TPS) provides a varying voltage signal depending on throttle valve angle. Signal voltage varies from about .50 volt at idle to 4.5 volts at wide open throttle. Each time TPS voltage drops to less than 1.25 volts and stops, ECM assumes this is zero degrees throttle angle and measures throttle percentage angle from this point.

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

1. This test confirms Code 21 and checks if fault is a hard failure or an intermittent condition. Code 21 will set if TPS voltage is greater than 2.5 volts 2-10 seconds with engine running. On 2.8L, Code 21 may set if MAP sensor signal less than 2 volts.
2. This test simulates conditions for Code 22. If ECM recognizes low voltage signal and sets Code 22, ECM and power and signal circuits are not at fault.
3. This step isolates a faulty sensor, ECM or an open ground circuit.

CODE 22, TPS SIGNAL VOLTAGE LOW

Throttle Position Sensor (TPS) provides a varying voltage signal depending on throttle valve angle. Signal voltage varies from less than about .50 volt at idle to 4.5 volts at wide open throttle.

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

1. This test confirms Code 22 and tests if fault is a hard failure or an intermittent condition. Code 22 will set if engine is running and TPS voltage is less than .2 volt for 2-4 seconds.
2. This simulates Code 21. If ECM recognizes a high voltage signal and sets Code 21, ECM and wiring are not at fault. Replace TPS.
3. This simulates a high voltage signal to check for on open TPS signal circuit.

CODE 24, VEHICLE SPEED SIGNAL LOW

The speed sensor circuit consists of a magnetic-induction sensor, Vehicle Speed Sensor (VSS) buffer, and wiring. Gear teeth on output shaft induce an alternating current in sensor. This signal is then transmitted to buffer. The buffer compensates for various axle ratios and converts signal into a square wave signal for use by the speedometer, cruise control ABS, and ECM.

The buffer sends 2 different signals to the ECM. circuit No. 437 relays transmission output speed, which is used to control shift points, line pressure torque converter clutch and DTC 24 and 72. Circuit No. 1716 relays vehicle speed which is used to control engine operating conditions and DTC 16. When DTC 24 sets, only 2nd gear at maximum line pressure will occur. DTC 24 sets when the following conditions are met for 6.4 seconds

1. Transmission is not in Park or Neutral.
2. Circuit No. 437 voltage is constant.
3. Engine speed is more than 3000 RPM.
4. Output speed less than 250 RPM.
5. Manifold absolute pressure 14.5-36.9 psi (100-255 kPa).
6. Throttle position 10-100 percent. NOTE: Test numbers refer to numbers on diagnostic chart.

1. This test monitors voltage on circuit No. 437. With wheels turning, the pulsating action causes a varying voltage. Voltage variation will be greater at low wheel speeds and an average of 4-6 volts at about 20 MPH.
2. Less than one volt at ECM connector indicates circuit No. 437 is shorted to ground. Disconnect circuit No. 437 at VSS buffer. If voltage now reads more than 10 volts, the VSS buffer is faulty. If voltage remains less than 10 volts, then circuit No. 437 is grounded. If circuit No. 437 is not grounded, check for a faulty ECM connector or ECM.
3. A steady 8-12 volt reading at the ECM connector indicates that circuit No. 437 is open or VSS buffer is faulty.

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 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.

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.

CODE 67, TCC SOLENOID CIRCUIT CHECK

The TCC solenoid is a normally open exhaust valve. The PCM will engage the solenoid by grounding circuit with an internal quad-driver.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks the ability of PCM to control solenoid.
2. This test checks for power, from the ignition through the fuse, to the TCC solenoid.

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. Checks the indicated range signal to the selected range. A faulty switch could set this code.
2. Checks TCC for slippage while in a commanded lock-up state.

CODE 72, VSS CKT LOSS TRANSMISSION OUTPUT SIGNAL - DIESEL

Note. For Code 72 coverage on gasoline models, see appropriate G - GASOLINE TESTS W/ CODES article in the ENGINE PERFORMANCE section. See below.

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)

VSS output sensor is a magnetic induction type. Gear teeth pressed on outside diameter of output carrier assembly induce an alternating current in sensor when drive wheels are turning.

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

1. Test verifies VSS voltage at PCM.
2. Test checks VSS buffer ground circuit.
3. Test checks VSS circuit at buffer module.
4. Test verifies VSS signal at sensor.

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 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.

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.

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.

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.