Automatic Transmission Diagnosis - 4L60-E: Other Chevrolet Silverado 2500

ADAPT FUNCTION

The 4L60-E transmission utilizes a line pressure control system during upshifts to compensate for the normal wear of transmission components. By adjusting the line pressure, the PCM can maintain acceptable transmission shift times. This process is known as adaptive learning or shift adapts and is similar to the closed loop fuel control system used for the engine.

In order for the PCM to perform a shift adapt, it must first identify if an upshift is acceptable to analyze. For example, upshifts that occur during cycling of the A/C compressor or under extreme throttle changes could cause the PCM to incorrectly adjust line pressure. When an upshift is initiated, a number of contingencies (such as throttle position, transmission temperature, and vehicle speed) are checked to determine if the actual shift time is valid to compare to a calibrated desired shift time. If all the contingencies are met during the entire shift, then the shift is considered valid and the adapt function may be utilized if necessary.

Once an adaptable shift is identified, the PCM compares the actual shift time to the desired shift time and calculates the difference between them. This difference is known as the shift error. The actual shift time is determined from the time that the PCM commands the shift to the start of the engine RPM drop initiated by the shift. If the actual shift time is longer than the calibrated desired shift time (a soft feel or slow engagement), then the PCM decreases current to the Pressure Control (PC) solenoid to increase line pressure for the next upshift under identical conditions. If the actual shift time is shorter than the calibrated desired shift time (a firm engagement), then the PCM increases current to the PC solenoid to decrease line pressure for the next upshift under identical conditions.

The purpose of the adapt function is to automatically compensate the shift quality for the various vehicle shift control systems. It is a continuous process that will help to maintain optimal shift quality throughout the life of the vehicle.

Clearing Transmission Adaptive Pressure

Transmission Adaptive Pressure (TAP) information is displayed and may be reset using a scan tool.

The adapt function is a feature of the PCM that either adds or subtracts line pressure from a calibrated base line pressure in order to compensate for normal transmission wear. The TAP information is divided into 13 units called cells. The cells are numbered 4 through 16. Each cell represents a given torque range. TAP cell 4 is the lowest adaptable torque range and TAP cell 16 is the highest adaptable torque range. It is normal for TAP cell values to display zero or negative numbers. This indicates that the PCM has adjusted line pressure at or below the calibrated base line pressure.

Updating TAP information is a learning function of the PCM designed to maintain acceptable shift times. It is not recommended that TAP information be reset unless one of the following repairs has been made: Transmission overhaul or replacement. Repair or replacement of an apply or release component (clutch, band, piston, servo). Repair or replacement of a component or assembly which directly affects line pressure.

Resetting the TAP values using a scan tool will erase all learned values in all cells. As a result, the PCM will need to relearn TAP values. Transmission performance may be affected as new TAPs are learned. Learning can only take place when the PCM has determined that an acceptable shift has occurred. The PCM must also relearn TAP values if it is replaced.

TRANSMISSION COMPONENTS & SYSTEMS

The mechanical components of the 4L60-E are as follows

1. Torque Converter Assembly
2. Servo Assembly And 2-4 Band Assembly
3. Reverse Input Clutch And Housing
4. Overrun Clutch
5. Forward Clutch
6. 3-4 Clutch
7. Forward Sprag Clutch Assembly
8. Lo And Reverse Roller Clutch Assembly
9. Lo And Reverse Clutch Assembly
10. Two Planetary Gear Sets: Input And Reaction
11. Oil Pump Assembly
12. Control Valve Body Assembly

The electrical components of the 4L60-E are as follows

1. 1-2 And 2-3 Shift Solenoid Valves
2. 3-2 Shift Solenoid Valve Assembly
3. Pressure Control (PC) Solenoid
4. Torque Converter Clutch (TCC) Solenoid Valve
5. TCC Pulse Width Modulation (PWM) Solenoid Valve
6. Transmission Fluid Pressure (TFP) Manual Valve Position Switch
7. Transmission Fluid Temperature (TFT) sensor
8. Vehicle Speed Sensor Assembly

1-2 & 2-3 Shift Solenoid Valves

Note. The manual valve hydraulically can override the shift solenoids. Only in "D4" do the shift solenoid states totally determine what gear the transmission is in. In the other manual valve positions, the transmission shifts hydraulically and the shift solenoid states catch up when the throttle position and the vehicle speed fall into the correct ranges.

The 1-2 and 2-3 shift solenoid valves (also called "A" and "B" solenoids) are identical devices that control the movement of the 1-2 and 2-3 shift valves (the 3-4 shift valve is not directly controlled by a shift solenoid). The solenoids are normally open exhaust valves that work in four combinations to shift the transmission into different gears. See SHIFT SOLENOID OPERATION table.

The PCM energizes each solenoid by grounding the solenoid through an internal quad driver. This sends current through the coil winding in the solenoid and moves the internal plunger out of the exhaust position. When ON, the solenoid redirects fluid to move a shift valve.

The PCM-controlled shift solenoids eliminate the need for T.V. and governor pressures to control shift valve operation.

SHIFT SOLENOID OPERATION

Pressure Control Solenoid

The Pressure Control (PC) solenoid is an electronic pressure regulator that controls pressure based on the current flow through its coil winding. The magnetic field produced by the coil moves the solenoid's internal valve which varies pressure to the pressure regulator valve.

The PCM controls the PC solenoid by commanding current between 0.1 and 1.1 amps. This changes the duty cycle of the solenoid, which can range between 5 percent and 95 percent (typically less than 60 percent). High amperage (1.1 amps) corresponds to minimum line pressure, and low amperage (0.1 amp) corresponds to maximum line pressure (if the solenoid loses power, the transmission defaults to maximum line pressure).

The PCM commands the line pressure values, using inputs such as engine speed and throttle position sensor voltage.

The PC solenoid takes the place of the throttle valve or the vacuum modulator that was used on past model transmissions.

Transmission Range Switch

The Transmission Range (TR) switch is part of the Park/Neutral Position (PNP) switch and backup lamp switch assembly, which is externally mounted on the transmission manual shaft. The TR switch contains four internal switches that indicate the transmission gear range selector lever position. The PCM supplies ignition voltage to each switch circuit. As the gear range selector lever is moved, the state of each switch may change, causing the circuit to open or close. An open circuit or switch indicates a high voltage signal. A closed circuit or switch indicates a low voltage signal. The PCM detects the selected gear range by deciphering the combination of the voltage signals. The PCM compares the actual voltage combination of the switch signals to a TR switch combination chart stored in memory.

TRANSMISSION RANGE SWITCH LOGIC (1)

Transmission In-Line 20-Pin Electrical Connector

The transmission electrical connector is an important part of the transmission operating system. Any interference with the electrical connection can cause the transmission to set DTCs or affect proper operation.

The following items can affect the electrical connection

1. Bent pins in the connector from rough handling during connection and disconnection.
2. Wires backing away from the pins or coming uncrimped, in either the internal or the external wiring harness.
3. Dirt contamination entering the connector when disconnected.
4. Pins in the internal wiring connector backing out of the connector or pushed out of the connector during re-connection.
5. Transmission fluid leaking into the connector, wicking up into the external wiring harness and degrading the wire insulation.
6. Moisture intrusion in the connector.
7. Low pin retention in the external connector from excessive connection and disconnection of the wiring connector assembly.
8. Pin corrosion from contamination.
9. Damaged connector assembly.

Remember the following points

1. To remove the connector, squeeze the two tabs toward each other and pull straight up without pulling by the wires.
2. Limit twisting or wiggling the connector during removal. Bent pins can occur.
3. Do not pry the connector off with a screwdriver or other tool.
4. Visually inspect the seals to ensure that they are not damaged during handling.
5. To reinstall the external wiring connector, first orient the pins by lining up the arrows on each half of the connector. Push the connector straight down into the transmission without twisting or angling the mating parts.
6. The connector should click into place with a positive feel and/or noise.
7. Whenever the transmission external wiring connector is disconnected from the internal harness and the engine is operating, DTCs will set. Clear these DTCs after reconnecting the external connector.

POWERTRAIN CONTROL MODULE

The PCM is the control center of the vehicle that controls the following

1. Fuel metering system.
2. Transmission shifting.
3. Ignition timing.
4. On-board diagnostics for powertrain functions.

For model specific PCM locations, see POWERTRAIN CONTROL MODULE under COMPONENT LOCATIONS.

The PCM supplies either 5 or 12 volts to power various sensors and switches. This is done through resistances in the PCM. The resistance is so high in value that a test light does not illuminate when connected to the circuit. In some cases, even an ordinary shop voltmeter does not give an accurate reading because the voltmeters resistance is too low. Therefore, a DVOM with a minimum of 10 megohms input impedance is required to ensure accurate voltage readings.

LIMP-IN MODE

If sensor input signals are missing or inadequate for transmission operation, PCM will output preset operating signals to transmission. This mode will keep vehicle operational and allow it to be driven with reduced transmission function and performance until a repair facility is reached. Malfunction Indicator Light (MIL) may illuminate if malfunction occurs. Vehicle should not be driven for extended periods in limp-in mode.

Note. Malfunction Indicator Light (MIL) located on instrument cluster is also referred to as SERVICE ENGINE SOON light.

ELECTRONIC CONTROL SYSTEM

The PCM constantly monitors the information from various sensors and controls the systems that affect vehicle performance and emissions. The PCM also performs the diagnostic functions for those systems. The PCM can recognize operational problems and alert the driver through the MIL when a malfunction has occurred. When a malfunction is detected, the PCM stores a Diagnostic Trouble Code (DTC) which helps to identify problem areas. This is done to aid the technician in making repairs.

SHIFT INTERLOCK SYSTEM

Note. For system description and repair information, see appropriate SHIFT INTERLOCK SYSTEMS article.

PCM/VCM LOCATION

Scheme 527

Electrical Function Check

Perform this check first, to ensure the electronic transmission components are connected and functioning properly. If these components are not checked, a simple electrical condition could be mis-diagnosed.

1. Connect the scan tool.
2. Ensure the gearshift lever is in Park and set the parking brake.
3. Start the engine.
4. Verify that the following scan tool data can be obtained and is functioning properly. Data that is questionable may indicate a concern. Engine Speed Transmission Output Speed Vehicle Speed Transmission Fluid Pressure (TFP) Manual Valve Position Switch Transmission Range Commanded Gear Pressure Control (PC) Solenoid Reference Current PC Solenoid Actual Current PC Solenoid Duty Cycle Brake Switch Engine Coolant Temperature Transmission Fluid Temperature Throttle Angle Ignition Voltage 1-2 Shift Solenoid 2-3 Shift Solenoid TCC Solenoid Duty Cycle TCC Slip Speed
5. Monitor the brake switch signal while depressing and releasing the brake pedal. The scan tool should display: CLOSED when the brake pedal is released. OPEN when the brake pedal is depressed.
6. Check the garage shifts in the following order: Apply the brake pedal and ensure the parking brake is set. Move the gearshift lever through the following ranges: Park to Reverse, Reverse to Neutral and Neutral to Drive. Pause 2-3 seconds in each gear position. Verify the gear engagements are immediate and not harsh.
7. Monitor transmission range on the scan tool engine list while performing the following: Apply the brake pedal and ensure the parking brake is set. Move the gearshift lever through all ranges. Pause 2-3 seconds in each range. Return gearshift lever to Park. Verify that all gearshift lever positions match the scan tool display.
8. Check throttle angle input in the following order: Apply the brake pedal and ensure the parking brake is set. Ensure the gearshift lever is in Park. Monitor throttle angle while increasing and decreasing engine speed with the throttle pedal. The scan tool throttle angle should increase and decrease with engine speed.

If any of the above checks do not perform properly, record the result for reference after completion of the road test.

Part Throttle Detent Downshift

1. Place the gearshift lever in the Overdrive position.
2. Accelerate the vehicle to 40-55 MPH in 4th gear.
3. Quickly increase throttle angle to greater than 50 percent.
4. Verify the TCC releases and transmission downshifts immediately to 3rd gear.

Full Throttle Detent Downshift

1. Place the gearshift lever in the Overdrive position.
2. Accelerate the vehicle to speeds of 40-55 MPH in 4th gear.
3. Quickly increase throttle angle to 100 percent.
4. Verify the TCC releases and the transmission downshifts immediately to 2nd gear.

Manual Downshifts

The shift solenoid valves do not control manual downshifts. All manual downshifts are hydraulic. The solenoid states will change during, or shortly after, a manual downshift is selected.

Manual 4-3 Downshift

1. Place the gearshift lever in the Overdrive position.
2. Accelerate the vehicle to 40-55 MPH in 4th gear.
3. Release the throttle while moving the gearshift lever to 3rd.
4. Verify the transmission downshifts immediately to 3rd gear and the engine slows the vehicle.

Manual 4-2 Downshift

1. Place the gearshift lever in the Overdrive position.
2. Accelerate the vehicle to 40-45 MPH.
3. Release the throttle while moving the gearshift lever to 2nd.
4. Verify the TCC releases, the transmission downshifts immediately to 2nd gear and the engine slows the vehicle.

Manual 4-1 Downshift

1. Place the gearshift lever in the Overdrive position.
2. Accelerate the vehicle to 30 MPH.
3. Release the throttle while moving the gearshift lever to 1st.
4. Verify the TCC releases the transmission immediately downshifts to 1st gear and the engine slows the vehicle.

Coasting Downshifts

1. Place the gearshift lever in the Overdrive position.
2. Accelerate the vehicle to 4th gear with the TCC applied.
3. Release the throttle and lightly apply the brakes.
4. Verify the TCC releases and downshifts occur at speeds shown in the shift speed chart. See «SHIFT SPEED SPECIFICATIONS»(ref-139572-S31749840592002050200000) .

Manual Gear Range Selection

The shift solenoids control the upshifts in the manual gear ranges. Perform the following tests using 10-15 percent throttle angle.

Reverse

1. With the vehicle stopped, move the gearshift lever to Reverse.
2. Slowly accelerate the vehicle.
3. Verify that there is no noticeable slip, noise or vibration.

Manual First

1. With the vehicle stopped, move the gearshift lever to 1st.
2. Accelerate the vehicle to 20 MPH.
3. Verify no upshifts occur, the TCC does not apply and there is no noticeable slip, noise, or vibration.

Manual Second

1. With the vehicle stopped, move the gearshift lever to 2nd.
2. Accelerate the vehicle to 35 MPH.
3. Verify the 1-2 shift occurs, the 2-3 shift does not occur and there is no noticeable slip, noise or vibration.

Manual Third

1. With the vehicle stopped, move the gearshift lever to 3rd.
2. Accelerate the vehicle to 40 MPH.
3. Verify the 1-2 shift occurs, the 2-3 shift occurs and there is no noticeable slip, noise or vibration.

Scheme 528

Scheme 529

Scheme 530

Scheme 531

Scheme 532

Scheme 533

Poor Acceleration At Low Speed

If the stator is freewheeling at all times, the vehicle tends to have poor acceleration from a standstill. At speeds above 30-35 MPH, the vehicle may act normally. For poor acceleration, you should first determine that the exhaust system is not blocked, and the transmission is in 1st gear when starting out.

If the engine freely accelerates to high RPM in Neutral, you can assume that the engine and the exhaust system are normal. Check for poor performance in Drive and Reverse to help determine if the stator is freewheeling at all times.

Poor Acceleration At High Speed

If the stator is locked up at all times, performance is normal when accelerating from a standstill. Engine RPM and vehicle speed are limited or restricted at high speeds. Visual examination of the converter may reveal a blue color from overheating.

If the converter has been removed, you can inspect the stator roller clutch by inserting a finger into the splined inner race of the roller clutch and trying to turn the race in both directions. You should be able to freely turn the inner race clockwise, but you should have difficulty in moving the inner race counterclockwise or you may be unable to move the race at all.

If Shudder Occurs After TCC has Applied

If shudder occurs after the TCC has applied, most of the time there is nothing wrong with the transmission.

As mentioned above, the TCC is not likely to slip after the TCC has been applied. Engine problems may go unnoticed under light throttle and load, but they become noticeable after the TCC apply when going up a hill or accelerating. This is due to the mechanical coupling between the engine and the transmission.

Once TCC is applied, there is no torque converter, fluid coupling, assistance. Engine or driveline vibrations could be unnoticeable before TCC engagement.

Inspect the following components to avoid misdiagnosis of TCC shudder. An inspection will also avoid the unnecessary disassembly of a transmission or the unnecessary replacement of a torque converter.

1. Spark Plugs Inspect for cracks, high resistance or a broken insulator.
2. Plug Wires Look in each end. If there is red dust (ozone) or a black substance (carbon) present, the wires are bad. Also look for a white discoloration of the wire. This indicates arcing during hard acceleration.
3. Coil Look for a black discoloration on the bottom of the coil. This indicates arcing while the engine is misfiring.
4. Fuel Injector The filter may be plugged.
5. Vacuum Leak The engine will not get a correct amount of fuel. The mixture may run rich or lean depending on where the leak occurs.
6. EGR Valve The valve may let in too much or too little unburnable exhaust gas and could cause the engine to run rich or lean.
7. MAP/MAF Sensor Like a vacuum leak, the engine will not get the correct amount of fuel for proper engine operation.
8. Carbon On Intake Valves Carbon restricts the proper flow of air/fuel mixture into the cylinders.
9. Flat Cam Valves do not open enough to let the proper fuel/air mixture into the cylinders.
10. Oxygen Sensor This sensor may command the engine too rich or too lean for too long.
11. Fuel Pressure This may be too low.
12. Engine Mounts Vibration of the mounts can be multiplied by TCC engagement.
13. Axle Joints Check for vibration.
14. TP Sensor The TCC apply and release depends on the TP sensor in many engines. If the TP sensor is out of specification, TCC may remain applied during initial engine loading.
15. Cylinder Balance Bad piston rings or poorly sealing valves can cause low power in a cylinder.
16. Fuel Contamination This causes poor engine performance.

HYDRAULIC PRESSURE TESTS

1. Before performing hydraulic pressure test, check fluid level and condition. Check manual control linkages for correct adjustment, and ensure engine is properly tuned.
2. Connect scan tool to Data Link Connector (DLC). Apply parking brake and start engine. Check for stored Diagnostic Trouble Codes (DTC). If DTCs are present, diagnose as necessary. Turn engine off. Connect oil pressure gauge to line pressure test port. (Scheme 534)or (Scheme 535).
3. Start engine and warm to normal operating temperature. With vehicle in Reverse, line pressure should be 64-324 psi (441-2234 kPa). With vehicle in Park, Neutral or Drive, line pressure should be 55-189 psi (379-1303 kPa).
4. Shift transaxle into Park. Access Pressure Control Solenoid (PCS) test on scan tool. Increase DESIRED PCS in.1 amp increments and read corresponding line pressure on oil pressure gauge. Allow pressure to stabilize for 5 seconds after each current change. Compare readings to specifications. See «LINE PRESSURE SPECIFICATIONS»(ref-139572-S34710988842002050700000) table. If pressure readings are not as specified, and no DTCs are present, an internal malfunction exists. See «SYMPTOM DIAGNOSIS»(ref-139572-S05930327492002050200000) under TROUBLE SHOOTING.

Note. Scan tool is only able to control PC solenoid in Park and Neutral with vehicle stopped. This protects clutches from extremely high or low pressures in Reverse and Drive.

LINE PRESSURE SPECIFICATIONS

Scheme 534

Scheme 535

CLUTCH & SERVO AIR CHECKS

Note. For additional information, refer to overhaul procedures. See appropriate OVERHAUL article.

SUMMARY

If no hard DTCs are present, and driveability symptoms or intermittent DTCs exist, attempt diagnosis by symptom, or by testing individual components related to system fault. See TROUBLE SHOOTING and/or COMPONENT TESTS .

Note. Always clear DTCs once repairs are complete. See CLEARING DIAGNOSTIC TROUBLE CODES . Road test vehicle and retrieve DTCs to determine if complaint or DTC is repaired.

Action Taken By PCM

PCM performs the following actions if DTC is set

1. Does not illuminate MIL.
2. Freezes shift adapts from being updated.
3. DTC P0218 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL.
2. Commands 2nd gear only.
3. Commands maximum line pressure.
4. Inhibits TCC engagement.
5. Freezes shift adapts from being updated.
6. Records operating conditions when conditions for running DTC are met.
7. DTC P0502 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL.
2. Commands a soft shift to 2nd gear.
3. Commands maximum line pressure.
4. Inhibits TCC engagement.
5. Inhibits 4th gear in hot mode.
6. Freezes shift adapts from being updated.
7. Records operating conditions when conditions for running DTC are met.
8. DTC P0503 is recorded in history.

PCM performs the following actions if DTC is set

1. Does not illuminate MIL.
2. Records operating conditions when conditions for running DTC are met.
3. DTC P0705 is recorded in history.

PCM performs the following actions if DTC is set

1. Does not illuminate MIL.
2. Records operating conditions when conditions for running DTC are met.
3. DTC P0706 is recorded in history.

PCM performs the following actions if DTC is set

1. Does not illuminate MIL.
2. Freezes shift adapts from being updated.
3. Determines and uses a default transmission fluid temperature based on certain operating criteria.
4. Records operating conditions when conditions for running DTC are met.
5. DTC P0711 is recorded in history.

PCM performs the following actions if DTC is set

1. Defaults transmission temperature to 275°F (135°C).
2. Freezes shift adapts from being updated.
3. Determines and uses a default transmission fluid temperature based on certain operating criteria.
4. Records operating conditions when conditions for running DTC are met.
5. DTC P0712 is recorded in history.

PCM performs the following actions if DTC is set

1. Calculates a default transmission fluid temperature based on engine coolant temperature, intake air temperature and engine run time.
2. Freezes shift adapts from being updated.
3. Determines and uses a default transmission fluid temperature based on certain operating criteria.
4. Records operating conditions when conditions for running DTC are met.
5. DTC P0713 is recorded in history.

PCM performs the following actions if DTC is set

1. Does not illuminate MIL.
2. PCM disregards brake switch input for TCC scheduling.
3. Records operating conditions when conditions for running DTC are met.
4. DTC P0719 is recorded in history.

PCM performs the following actions if DTC is set

1. Does not illuminate MIL.
2. Records operating conditions when conditions for running DTC are met.
3. DTC P0724 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL at second consecutive failure signal.
2. Inhibits TCC engagement.
3. Inhibits 4th gear if in hot mode.
4. Freezes shift adapts from being updated.
5. Records operating conditions when conditions for running DTC are met.
6. DTC P0740 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL at second consecutive failure signal.
2. Commands maximum line pressure.
3. Commands TCC off.
4. Freezes shift adapts from being updated.
5. Records operating conditions when conditions for running DTC are met.
6. DTC P0741 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL at second consecutive failure signal.
2. Freezes shift adapts from being updated.
3. Records operating conditions when conditions for running DTC are met.
4. DTC P0742 is recorded in history.

PCM performs the following actions if DTC is set

1. Does not illuminate MIL.
2. PC solenoid valve is off.
3. Freezes shift adapts from being updated.
4. Records operating conditions when conditions for running DTC are met.
5. DTC P0748 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL.
2. Commands "D2" line pressure.
3. Freezes shift adapts from being updated.
4. Records operating conditions when conditions for running DTC are met.
5. DTC P0751 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL.
2. Commands "D2" line pressure.
3. PCM inhibits 3-2 downshifts if vehicle speed is greater than 30 MPH.
4. Freezes shift adapts from being updated.
5. Records operating conditions when conditions for running DTC are met.
6. DTC P0752 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL during the second consecutive trip in which the conditions for setting the DTC are met.
2. PCM commands "D2" line pressure.
3. PCM inhibits 3-2 downshifts if vehicle speed is greater than 30 MPH.
4. Freezes shift adapts from being updated.
5. Records operating conditions when conditions for running DTC are met.
6. DTC P0753 is recorded in history.

SHIFT SOLENOID COMBINATIONS & GEAR RATIO

PCM performs the following actions if DTC is set

1. Illuminates MIL.
2. Commands 3rd gear only.
3. Commands maximum line pressure.
4. Inhibits TCC engagement.
5. Freezes shift adapts from being updated.
6. Records operating conditions when conditions for running DTC are met.
7. DTC P0756 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL.
2. Commands 3rd gear only.
3. Commands maximum line pressure.
4. Inhibits TCC engagement.
5. Freezes shift adapts from being updated.
6. Records operating conditions when conditions for running DTC are met.
7. DTC P0757 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL.
2. Commands 3rd gear only.
3. PCM commands maximum line pressure.
4. Inhibits TCC engagement.
5. Freezes shift adapts from being updated.
6. Records operating conditions when conditions for running DTC are met.
7. DTC P0758 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL.
2. Commands soft landing into 3rd gear.
3. PCM commands maximum line pressure.
4. Inhibits TCC engagement.
5. Inhibits 4th gear if transmission is in hot mode.
6. Freezes shift adapts from being updated.
7. Records operating conditions when conditions for running DTC are met.
8. DTC P0785 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL.
2. Commands "D2" line pressure.
3. Commands "D4" shift pattern.
4. Freezes shift adapts from being updated.
5. Records operating conditions when conditions for running DTC are met.
6. DTC P1810 is recorded in history.

PCM performs the following action if DTC is set

1. Illuminates MIL.
2. Inhibits TCC engagement.
3. Inhibits 4th gear if transmission is in hot mode.
4. Freezes shift adapts from being updated.
5. Records operating conditions when conditions for running DTC are met.
6. DTC P1860 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL at second consecutive failure signal.
2. Commands maximum line pressure.
3. Inhibits TCC engagement.
4. Inhibits 4th gear if transmission is in hot mode.
5. Freezes shift adapts from being updated.
6. Records operating conditions when conditions for running DTC are met.
7. DTC P1870 is recorded in history.

PCM performs the following actions if DTC is set

1. Illuminates MIL.
2. Commands a normal shift pattern.
3. Records operating conditions when conditions for running DTC are met.
4. DTC P1875 is recorded in history.

RANGE SELECTOR DISPLAY INOPERATIVE OR DISPLAYS INCORRECT RANGE

Note. For circuit identification, see CONNECTOR IDENTIFICATION and WIRING DIAGRAMS .

2ND GEAR START SWITCH INDICATOR LIGHT - ALWAYS ON OR INOPERATIVE

Note. For circuit identification, see CONNECTOR IDENTIFICATION and WIRING DIAGRAMS .

Note. Camaro and Firebird with 3.8L engine are equipped with a 2nd gear start switch. Switch does not set a DTC. However, this component may affect transmission performance.

COMPONENT RESISTANCE

Connect DVOM between specified terminals at component or at transmission in-line 20-pin connector to transmission. Measure individual component resistance at specified temperature. (Scheme 536) See COMPONENT RESISTANCE SPECIFICATIONS table. If resistance is not as specified, replace appropriate component.

COMPONENT RESISTANCE SPECIFICATIONS

Scheme 536

Scheme 537