Automatic Transmission Diagnosis - 4L80-E: Other Chevrolet Silverado 2500

GEAR RATIOS

TRANSMISSION GEAR RATIOS

ADAPT FUNCTION

The 4L80-E transmission uses a line pressure control system that has the ability to adapt line pressure to compensate for normal wear of the following parts

1. The clutch fiber plates.
2. The springs and seals.
3. The apply bands.

This adaptive feature is similar to the fuel and idle control systems, where the PCM has the ability to learn and adjust for monitored system changes.

The PCM maintains information for the following transmission adaptive systems

1-2, 2-3 & 3-4 Upshift Adapts

The PCM monitors the transmission Input Speed Sensor (ISS) and the Output Speed Sensor (OSS) to determine when the transmission has started and completed an upshift. The PCM looks at the time from the beginning, until the completion of the upshift. If the time of the upshift was longer than a calibrated value, then the PCM adjusts the current to the Pressure Control (PC) solenoid to increase line pressure for the next upshift under identical conditions. If the time of the upshift was shorter than a calibrated value, then the PCM adjusts the current to the PC solenoid to decrease line pressure for the next upshift under identical conditions.

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

1. Transmission overhaul or replacement.
2. Repair or replacement of an apply or release component.
3. 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 this unit are as follows

1. Torque converter with a torque converter clutch.
2. Gear type oil pump.
3. Five multiple disk clutches.
4. Two band assemblies.
5. Three planetary gear sets.
6. One sprag clutch.
7. Two roller clutches.
8. Control valve body assembly.

The electrical components of this unit are as follows

1. Two shift solenoid valves: 1-2 and 2-3.
2. Torque Converter Clutch (TCC) solenoid valve.
3. Pressure Control (PC) solenoid valve.
4. Transmission Fluid Temperature (TFT) sensor.
5. Transmission Fluid Pressure (TFP) manual valve position switch assembly.
6. Output Speed Sensor (OSS).
7. Input Speed Sensor (ISS).

ELECTRONIC COMPONENTS

Note. To locate transmission solenoids, sensors and switches, refer to illustration. (Scheme 164)

Pressure Control Solenoid Valve

The Pressure Control (PC) solenoid valve is attached to the valve body. The valve controls line pressure by moving a pressure regulator valve against spring pressure. The PC solenoid valve takes the place of the throttle valve or the vacuum modulator, which was used on past model transmissions.

The PCM varies line pressure based on engine load. Engine load is calculated from various inputs, especially the TP sensor switch. Line pressure is actually varied by changing the amperage applied to the PC solenoid valve from zero amps (high pressure) to 1.1 amps (low pressure). The PC solenoid valve current is periodically pulsed to prevent contamination from sticking to the pressure regulator valve.

One diagnostic code is associated with the PC solenoid valve. DTC P0748 sets when the PCM detects a difference of 0.16 amp or more between the amperage commanded and actual amperage. While the DTC is set, the PC solenoid valve turns off. Recovery can occur after the next ignition cycle. DTC P0748 does not sense a hydraulic problem such as a stuck valve.

1-2 Shift Solenoid Valve

The 1-2 shift solenoid valve is a normally open exhaust valve that is attached to the valve body. The PCM controls the solenoid by grounding the solenoid through an internal quad driver. The 1-2 shift solenoid valve is on in 1st and 4th gear. When commanded on, the 1-2 shift solenoid valve redirects fluid to act on the 1-2 shift valve. See SHIFT SOLENOID VALVE STATE & GEAR RATIO table.

There are 2 PCM related DTCs associated with the 1-2 shift solenoid valve: P0751 and P0753.

The PCM monitors the 1-2 shift solenoid circuit for an open or short to ground condition. If the PCM detects an open or short to ground condition, then DTC P0753 sets. If the PCM detects an incorrect gear ratio, then DTC P0751 sets. When DTC P0753 or P0751 sets, the PCM commands maximum line pressure, freezes shift adapts from being updated, and inhibits 3-2 downshifts.

2-3 Shift Solenoid Valve

The 2-3 shift solenoid valve is a normally open exhaust valve that is attached to the valve body. The PCM controls the solenoid by grounding the solenoid through an internal quad driver. The 2-3 shift solenoid valve is on in 3rd and 4th gear. When commanded on, the 2-3 shift solenoid valve redirects fluid to act on the 2-3 shift valve. See SHIFT SOLENOID VALVE STATE & GEAR RATIO table.

There are 2 PCM related DTCs associated with the 2-3 shift solenoid valve: P0756 and P0758.

The PCM monitors the 2-3 shift solenoid circuit for an open or short to ground condition. If the PCM detects an open or short to ground condition, then DTC P0758 sets. If the PCM detects an incorrect gear ratio, then DTC P0756 sets. When DTC P0758 or P0756 sets, the PCM commands maximum line pressure, freezes shift adapts from being updated, and inhibits 3-2 downshifts.

SHIFT SOLENOID VALVE STATE & GEAR RATIO

Input Speed & Output Speed Sensors

Both the Input Speed Sensor (ISS) and the Output Speed Sensor (OSS) are magnetic induction sensors. The input and the output sensors are accessible from the left hand side of the transmission. The ISS is located just forward of center, and the OSS sensor is located near the rear. A voltage signal is induced in the ISS by serrations, which are cut in the outside diameter of the forward clutch housing. Voltage is induced in the output sensor by gear teeth, which are pressed on the outside diameter of the rear carrier assembly.

The PCM uses speed information from these sensors to determine the following

1. Whether the engine is running.
2. Vehicle speed.
3. Calculation of the gear ratio.
4. Calculation of TCC slip.
5. Calculation of turbine speed.

DTC P0502 and P0503 set if a fault exists in the OSS sensor circuit, and the PCM calculates a default value using the ISS values. As long as the fault remains, and the DTC is set, the PCM also commands maximum line pressure, freeze shift adapts, and the MIL illuminates. If the fault is removed, normal operation resumes after the next ignition cycle.

Transmission Range Switch

The Transmission Range (TR) switch is part of the Park/Neutral Position (PNP) and backup lamp switch assembly, which is externally mounted on the transmission manual shaft. The TR switch contains 4 internal switches that indicate the transmission gearshift lever position. The PCM supplies ignition voltage to each switch circuit. As the gearshift 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. See TRANSMISSION RANGE SWITCH LOGIC table.

TRANSMISSION RANGE SWITCH LOGIC (1)

Transmission 20-Way In-Line 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 2 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.

Scheme 164

POWERTRAIN CONTROL MODULE

The Powertrain Control Module (PCM) is located in the engine compartment. 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.

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 voltmeter's 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 Malfunction Indicator Lamp (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.

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 Input Speed Transmission Output Speed Vehicle Speed Transmission Fluid Pressure (TFP) Manual Valve Position Switch Transmission Range 4WD Low 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 40 MPH.
3. Release the throttle while moving the gearshift lever to 1st.
4. Verify the TCC releases, 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-133047-S09044767142002021200000) .

Manual Gear Range Selection

The shift solenoids control the upshifts in the manual gear ranges.

Perform the following tests using 10 percent to 15 percent throttle angle.

1. Reverse 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.

1. Manual First 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.

1. Manual Second 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.

1. Manual Third 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 165

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

Note. Before performing a line pressure check, verify that the pressure control solenoid for the transmission is receiving the correct electrical signal from the PCM.

Note. After performing line pressure test, the transmission may experience harsh, soft or mushy shifts for up to 2 days later.

Line Pressure

Line pressures are calibrated for 2 sets of gear ranges: Drive, Park, Neutral and Reverse. This allows the transmission line pressure to be appropriate for different pressure needs in different gear ranges. See LINE PRESSURE RANGE SPECIFICATIONS table.

1. Install a scan tool.
2. Start the engine and set the parking brake.
3. Check for DTCs, including the DTC for a pressure control solenoid.
4. Repair the vehicle if necessary. Include the following areas: Inspect the fluid level. Inspect the manual linkage at the transmission.
5. Install or connect the scan tool.
6. Install or connect the Pressure Gauge (J-21867) at the line pressure tap. (Scheme 166)
7. Put the gearshift lever in Park and set the parking brake.
8. Start the engine and allow the engine to warm up at idle.
9. Access the OVERRIDE PRESSURE CONTROL SOLENOID test on the scan tool.
10. Increase the Pressure Control (PC) solenoid current in 0.1 amp increments. Read the corresponding line pressure on the pressure gauge. Allow the pressure to stabilize for 5 seconds after each current change.
11. Compare your data to the line pressure specifications. See «LINE PRESSURE SPECIFICATIONS»(ref-133047-S09246696342001112800000) table.
12. Remove the pressure gauge.
13. Apply pipe thread sealant with Teflon (GM P/N 12346004) to the line pressure tap plug. Install the line pressure tap plug. Tighten plug to specification. See «TORQUE SPECIFICATIONS»(ref-133047-S02990839492002021300000).

If your pressure readings differ greatly from the line pressure table, see SYMPTOM DIAGNOSIS under TROUBLE SHOOTING.

The scan tool is only able to control the pressure control solenoid in Park and Neutral with the vehicle stopped at idle. This protects the clutches from extremely high or low pressures in Drive or Reverse ranges.

LINE PRESSURE RANGE SPECIFICATIONS

LINE PRESSURE SPECIFICATIONS

Scheme 166

CLUTCH & SERVO AIR CHECKS

Note. For clutch and servo air check 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 . If no problem is found, verify proper electronic control system circuit operation.

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. Tow/Haul mode will be inoperative.

PCM performs the following actions if DTC is set

1. The PCM does not illuminate the MIL.
2. The PCM freezes shift adapts from being updated.
3. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as failure records.
4. The PCM stores DTC P0218 in PCM history.

PCM performs the following actions if DTC is set

1. For California emission equipped vehicles, the PCM illuminates the MIL during the second consecutive trip in which the conditions for setting the DTC are met. For Non-California emission equipped vehicles, the MIL is not illuminated.
2. The PCM commands maximum line pressure.
3. The PCM freezes the shift adapts.
4. The PCM defaults a calculated output speed value by using the ISS values.
5. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
6. The PCM stores the DTC P0502 in PCM history during the second consecutive trip (California) or the first trip (Federal) in which the conditions for setting the DTC are met.

PCM performs the following actions if DTC is set

1. For California emission equipped vehicles, the PCM illuminates the MIL during the second consecutive trip in which the conditions for setting the DTC are met. For Non-California emission equipped vehicles, MIL is not illuminated.
2. The PCM commands maximum line pressure.
3. The PCM freezes the shift adapts.
4. The PCM defaults a calculated output speed value by using the input shaft speed values.
5. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
6. The PCM stores the DTC P0503 in PCM history during the second consecutive trip (California) or the first trip (Federal) in which the conditions for setting the DTC are met.

PCM performs the following actions if DTC is set

1. The PCM will use Transmission Fluid Pressure (TFP) switch to determine gear range.
2. The PCM does not illuminate the MIL.
3. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as failure records.
4. The PCM stores DTC P0706 in PCM history.

PCM performs the following actions if DTC is set

1. The PCM does not illuminate the MIL.
2. The PCM commands increased line pressure.
3. The PCM freezes shift adapts.
4. The PCM determines a default transmission temperature using the following matrix: If the engine run time is less than 60 seconds, then default transmission fluid temperature equals 117°F (47°C). If engine coolant temperature is less than 68°F (20°C), intake air temperature is used. If the engine coolant temperature is 68-230°F (20-110°C), then default transmission fluid temperature equals engine coolant temperature. If the engine coolant temperature is greater than 230°F (110°C), then default transmission fluid temperature is set to 284°F (140°C) and transmission shift pattern is in hot mode. If engine coolant temperature and transmission fluid temperature DTCs are both set, then default transmission fluid temperature is 284°F (140°C).
5. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as failure records.
6. The PCM stores DTC P0711 in PCM history.

PCM performs the following actions if DTC is set

1. The PCM does not illuminate the MIL.
2. The PCM commands increased line pressure.
3. The PCM freezes shift adapts.
4. The PCM determines a default transmission fluid temperature using the following matrix: If the engine run time is less than 60 seconds, then default transmission fluid temperature equals 117°F (47°C). If engine coolant temperature is less than 68°F (20°C), intake air temperature is used. If the engine coolant temperature is 68-230°F (20-110°C), then default transmission fluid temperature equals engine coolant temperature. If the engine coolant temperature is greater than 230°F (110°C), then default transmission fluid temperature is set to 284°F (140°C) and transmission shift pattern is in hot mode. If engine coolant temperature and transmission fluid temperature DTCs are both set, then default transmission fluid temperature is 284°F (140°C).
5. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as failure records.
6. The PCM stores DTC P0712 in PCM history.

PCM performs the following actions if DTC is set

1. The PCM does not illuminate the MIL.
2. The PCM commands increased line pressure.
3. The PCM freezes shift adapts.
4. The PCM determines a default transmission fluid temperature using the following matrix: If the engine run time is less than 60 seconds, then default transmission fluid temperature equals 117°F (47°C). If engine coolant temperature is less than 68°F (20°C), intake air temperature is used. If the engine coolant temperature is 68-230°F (20-110°C), then default transmission fluid temperature equals engine coolant temperature. If the engine coolant temperature is greater than 230°F (110°C), then default transmission fluid temperature is set to 284°F (140°C) and transmission shift pattern is in hot mode. If engine coolant temperature and transmission fluid temperature DTCs are both set, then default transmission fluid temperature is 284°F (140°C).
5. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as failure records.
6. The PCM stores DTC P0713 in PCM history.

PCM performs the following actions if DTC is set

1. The PCM illuminates the MIL during the second consecutive trip for all California emission equipped vehicles in which the conditions for setting the DTC are met.
2. The PCM commands maximum line pressure.
3. The PCM freezes shift adapts.
4. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
5. The PCM stores the DTC P0716 in PCM history during the second consecutive trip (California) or the first trip (Federal) in which the conditions for setting the DTC are met.

PCM performs the following actions if DTC is set

1. For California emission equipped vehicles, the PCM illuminates the MIL during the second consecutive trip in which the conditions for setting the DTC are met. For Non-California emission equipped vehicles, the MIL is not illuminated.
2. The PCM defaults the transmission to maximum line pressure.
3. The PCM freezes shift adapts.
4. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
5. The PCM stores the DTC P0717 in PCM history during the second consecutive trip (California) or the first trip (Federal) in which the conditions for setting the DTC are met.

PCM performs the following actions if DTC is set

1. The PCM does not illuminate the MIL.
2. For TCC scheduling, the PCM disregards the brake switch state if the TP sensor is greater than 1.5 percent and the vehicle speed is greater than 20 MPH.
3. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as failure records.
4. The PCM stores DTC P0719 in PCM history.

PCM performs the following actions if DTC is set

1. The PCM does not illuminate the MIL.
2. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as failure records.
3. The PCM stores DTC P0724 in PCM history.

PCM performs the following actions if DTC is set

1. The PCM does not illuminate the MIL.
2. The PCM commands maximum line pressure.
3. The PCM freezes shift adapts.
4. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as failure records.
5. The PCM stores DTC P0730 in PCM history.

PCM performs the following actions if DTC is set

1. For California emission equipped vehicles, the PCM illuminates the MIL during the second consecutive trip in which the conditions for setting the DTC are met. For Non-California emission equipped vehicles, the MIL is not illuminated.
2. The PCM inhibits the TCC.
3. The PCM increases line pressure.
4. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
5. The PCM stores the DTC P0741 in PCM history during the second consecutive trip (California) or the first trip (Federal) in which the conditions for setting the DTC are met.

PCM performs the following actions if DTC is set

1. For California emission equipped vehicles, the PCM illuminates the MIL during the second consecutive trip in which the conditions for setting the DTC are met. For Non-California emission equipped vehicles, the MIL is not illuminated.
2. The PCM commands maximum line pressure.
3. The PCM freezes shift adapts.
4. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
5. The PCM stores the DTC P0742 in PCM history during the second consecutive trip (California) or the first trip (Federal) in which the conditions for setting the DTC are met.

Action Taken PCM

PCM performs the following actions if DTC is set

1. The PCM does not illuminate the MIL.
2. The PCM disables the PC solenoid valve, defaulting the transmission to maximum line pressure.
3. The PCM freezes shift adapts.
4. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as failure records.
5. The PCM stores DTC P0748 in PCM history.

PCM performs the following actions if DTC is set

1. For California emission equipped vehicles, the PCM illuminates the MIL during the second consecutive trip in which the conditions for setting the DTC are met. For Non-California emission equipped vehicles, the MIL is not illuminated.
2. The PCM commands maximum line pressure.
3. The PCM freezes shift adapts.
4. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
5. The PCM stores the DTC P0751 in PCM history during the second consecutive trip (California) or the first trip (Federal) in which the conditions for setting the DTC are met.

PCM performs the following actions if DTC is set

1. For California emission equipped vehicles, the PCM illuminates the MIL during the second consecutive trip in which the conditions for setting the DTC are met. For Non-California emission equipped vehicles, the MIL is not illuminated.
2. The PCM commands maximum line pressure.
3. The PCM inhibits 3-2 downshifts above 25 MPH.
4. The PCM freezes shift adapts.
5. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
6. The PCM stores the DTC P0752 in PCM history during the second consecutive trip (California) or the first trip (Federal) in which the conditions for setting the DTC are met.

PCM performs the following actions if DTC is set

1. For California emission equipped vehicles, the PCM illuminates the MIL during the second consecutive trip in which the conditions for setting the DTC are met. For Non-California emission equipped vehicles, the MIL is not illuminated.
2. The PCM commands maximum line pressure.
3. The PCM freezes shift adapts.
4. The PCM inhibits 3-2 downshifts above 25 MPH.
5. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
6. The PCM stores the DTC P0753 in PCM history during the second consecutive trip (California) or the first trip (Federal) in which the conditions for setting the DTC are met.

PCM performs the following actions if DTC is set

1. The PCM illuminates the MIL for California emissions vehicles.
2. The PCM commands a soft landing to 2nd gear.
3. The PCM commands maximum line pressure.
4. The PCM freezes shift adapts.
5. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
6. The PCM stores DTC P0756 in PCM history.

PCM performs the following actions if DTC is set

1. The PCM illuminates the MIL for California emissions vehicles.
2. The PCM commands a soft landing to 2nd gear.
3. The PCM commands maximum line pressure.
4. The PCM freezes shift adapts.
5. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
6. The PCM stores DTC P0757 in PCM history.

PCM performs the following actions if DTC is set

1. The PCM illuminates the MIL for California emission vehicles.
2. The PCM commands a soft landing to 2nd gear.
3. The PCM commands maximum line pressure.
4. The PCM freezes shift adapts from being updated.
5. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
6. The PCM stores DTC P0758 in PCM history.

PCM performs the following actions if DTC is set

1. For California emission equipped vehicles, the PCM illuminates the MIL during the second consecutive trip in which the conditions for setting the DTC are met. For Non-California emission equipped vehicles, the MIL is not illuminated.
2. The PCM commands maximum line pressure.
3. The PCM assumes D4 for the PRNDL shift pattern.
4. The PCM freezes shift adapts.
5. The PCM forces the TCC on in 4th gear.
6. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
7. The PCM stores the DTC P1810 in PCM history during the second consecutive trip (California) or the first trip (Federal) in which the conditions for setting the DTC are met.

PCM performs the following actions if DTC is set

1. For California emission equipped vehicles, the PCM illuminates the MIL during the second consecutive trip in which the conditions for setting the DTC are met.
2. The PCM inhibits TCC engagement.
3. The PCM commands increased line pressure.
4. The PCM freezes shift adapts from being updated.
5. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
6. The PCM stores DTC P1860 in PCM history.

PCM performs the following actions if DTC is set

1. For California emission equipped vehicles, the PCM illuminates the MIL during the second consecutive trip in which the conditions for setting the DTC are met. For Non-California emission equipped vehicles, the MIL is not illuminated.
2. The PCM commands maximum line capacity.
3. The PCM inhibits the TCC engagement.
4. The PCM freezes shift adapts.
5. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
6. The PCM stores the DTC P1870 in PCM history during the second consecutive trip (California) or the first trip (Federal) in which the conditions for setting the DTC are met.

PCM performs the following actions if DTC is set

1. The PCM assumes a 4WD Low state if measured transfer case ratio is between 2.68 and 2.76.
2. The PCM assumes a non-4WD Low state if the measured transfer case ratio is between .95 and 1.05.
3. The PCM freezes shift adapts from being updated.
4. The PCM records the operating conditions when the conditions for setting the DTC are met. The PCM stores this information as freeze frame (California only) and failure records (California and Federal).
5. The PCM stores the DTC P1875 in PCM history during the second consecutive trip (California) or the first trip (Federal) in which the conditions for setting the DTC are met.

RANGE SELECTOR DISPLAY INOPERATIVE OR DISPLAYS INCORRECT RANGE

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

TOW/HAUL SWITCH/INDICATOR ALWAYS ON OR INOPERATIVE

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

Note. Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM module connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent contaminant intrusion into the PCM.

Note. The replacement PCM will not be programmed. DTC P0601 and P0602 indicate the EEPROM is not programmed or has malfunctioned.

SOLENOID VALVES

For replacement procedures for the following solenoids

1. 1-2 Shift Solenoid Valve
2. 2-3 Shift Solenoid Valve
3. Torque Converter Clutch (TCC) Solenoid Valve
4. Pressure Control (PC) Solenoid Valve

See appropriate AUTOMATIC article in TRANSMISSION SERVICING.

TFP MANUAL VALVE POSITION SWITCH

Note. Removal and installation procedure of the transmission fluid pressure manual valve position switch is contained within the valve body removal and installation procedure. See appropriate AUTOMATIC article in TRANSMISSION SERVICING.

TFT SENSOR

Note. Transmission fluid temperature sensor is part of transmission internal wire harness. For removal and installation procedure, see TRANSMISSION INTERNAL WIRING HARNESS .

SPEED SENSORS

Note. Removal and installation of vehicle speed sensor and input speed sensor is an un-bolt and bolt-on procedure. Only torque specifications are given. See TORQUE SPECIFICATIONS .

COMPONENT RESISTANCE

Connect DVOM between specified terminals at component or at transmission in-line 20-way connector to transmission. Measure individual component resistance at specified temperature. (Scheme 169) See COMPONENT RESISTANCE SPECIFICATIONS table. If resistance is not as specified, replace appropriate component. (Scheme 164)

COMPONENT RESISTANCE SPECIFICATIONS

Scheme 167

Scheme 168

Scheme 169

Scheme 170

Scheme 171

Scheme 172

Scheme 173

Scheme 174

Scheme 175

Scheme 176

Scheme 177

Scheme 178

Scheme 179

Scheme 180

Scheme 181

Scheme 182

Scheme 183

Scheme 184

Scheme 185

Scheme 186

Scheme 187

Scheme 188

Scheme 189

Scheme 190

Scheme 191

Scheme 192

Scheme 193

Transmission Electronic Control System Wiring Diagram (Sierra, Sierra HD, Silverado, Silverado HD, Suburban & Yukon XL - 6.0L). Scheme 194

Transmission Electronic Control System Wiring Diagram (Avalanche, Suburban & Yukon XL - 8.1L). Scheme 195