Automatic Transmission - 4L80-E/4L85-E (Service & Replacement): Other Chevrolet Suburban X

Type A

This DTC is emissions related. The PCM stores the DTC in History, Freeze Frame and Failure Records during the first trip in which the conditions for setting the DTC are met. The PCM also illuminates the malfunction indicator lamp (MIL) during the first trip in which the conditions for setting the DTC are met.

Type B

This DTC is emissions related. The PCM stores the DTC in Failure Records during the first trip in which the conditions for setting the DTC are met. The PCM stores the DTC in History and Freeze Frame during the second consecutive trip in which the conditions for setting the DTC are met. The PCM also illuminates the MIL during the second consecutive trip in which the conditions for setting the DTC are met.

Type C

This DTC is non-emissions related. The PCM stores the DTC in History and Failure Records during the first trip in which the conditions for setting the DTC are met. The PCM does not store the DTC in Freeze Frame and does not illuminate the MIL. For some type C DTCs, a message may be displayed on a DIC, if equipped. For other type C DTCs, a separate service lamp, other than the MIL, may be illuminated. Type C DTCs that do not display a message on the DIC or illuminate a separate service lamp were formerly referred to as type D.

Type X

This DTC is available in the PCM software, but has been disabled, or turned off. In this case, the diagnostic does not run, DTCs are not stored, and the MIL does not illuminate. Type X DTCs are used primarily for export vehicles that do not require MIL illumination or DTC storing.

The service information contained in this manual refers to the domestic, federal, calibration package. Domestic calibrations apply to vehicles sold in the United States, Canada and Japan. Export calibrations exist for both leaded and unleaded vehicles. DTC types may change for some export vehicles, and some DTCs may be turned off for leaded export vehicles. Differences between domestic and export calibrations are not reflected on DTC support information pages. DTC types for export calibrations are referenced only in the Diagnostic Trouble Code List/Type.

Condition 1

The TFT has not changed more than 2.25°C (4°F), in more than 80 seconds. No TFT change.

Condition 2

The TFT has an unrealistic temperature change of more than 20°C (36°F) 14 times in 7 seconds.

1. The TCC slip speed is 100-550 for 10 seconds.
2. All conditions for running the DTC are met for three occurrences.

1. The TCC slip speed is 100-550 for 10 seconds, the PCM commands maximum line pressure.
2. The TCC slip speed is 100-550 for 12.5 seconds, the PCM commands the TCC Off for 2 seconds.
3. The TCC slip speed is 100-550 for 15 seconds.

1. The engine speed is greater than 400 RPM for 7 seconds.
2. The PCM detects an illegal TFP manual valve position switch state for 60 seconds.

1. The engine speed is less than 50 RPM for 0.3 second; then 50-525 RPM for 0.025 second; then the engine speed is greater than 525 RPM.
2. The vehicle speed is less than 8 km/h (5 mph).
3. Engine RPM sequence must occur within 30 seconds of key on.
4. The PCM detects the gear range D2, D4 or REVERSE before and after start up.
5. All conditions are met for 7 seconds and AT ISS is greater than 200 RPM.

Condition 3

1. The vehicle speed is greater than 8 km/h (5 mph).
2. The throttle angle is greater than 10 percent.
3. The PCM detects an invalid state of the TFP sensor or the TFP circuit.
4. The TFP switch indicates the following: P/N when the ratio indicates third or fourth gear for greater than 15 seconds. Reverse when the ratio indicates D4, D3, D2, and D1 for greater than 15 seconds. D4, D3, D2, and D1 when the ratio indicates reverse for greater than 7 seconds.

Electrical Function Check

Perform this check first, in order 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 gear selector 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. Refer to Transmission Scan Tool Data List, See «Transmission Scan Tool Data List»(ref-180352-S19661381442005092800000) for typical data values. Data that is questionable may indicate a concern. Engine speed Transmission input speed, turbine Transmission output speed Vehicle speed TFP manual valve position switch Transmission range, engine list 4WD low Commanded gear 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 6.1. Apply the brake pedal and ensure the parking brake is set. 6.2. Move the gear selector through the following ranges: 6.2.1. PARK to REVERSE 6.2.2. REVERSE to NEUTRAL 6.2.3. NEUTRAL to DRIVE 6.3. Pause 2-3 seconds in each gear position. 6.4. Verify the gear engagements are immediate and not harsh. Important: Harsh engagement may be caused by any of the following conditions: High idle speed Compare engine idle speed to desired idle speed. Commanded low PC solenoid current compare PC solenoid reference current to PC solenoid actual current. A default condition caused by certain DTCs that result in maximum line pressure to prevent slippage Important: Soft or delayed engagement may be caused by any of the following conditions: Low idle speed Compare engine idle speed to desired idle speed. Low fluid level Commanded high PC solenoid current compare PC solenoid reference current to PC solenoid actual current. Cold transmission fluid Check for low transmission fluid temperature.
7. Monitor transmission range on the scan tool, engine list. 7.1. Apply the brake pedal and ensure the parking brake is set. 7.2. Move the gear selector through all ranges. 7.3. Pause 2-3 seconds in each range. 7.4. Return gear selector to PARK. 7.5. Verify that all selector positions match the scan tool display.
8. Check throttle angle input. 8.1. Apply the brake pedal and ensure the parking brake is set. 8.2. Ensure the gear selector is in PARK. 8.3. Monitor throttle angle while increasing and decreasing engine speed with the throttle pedal. The scan tool throttle analog 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 gear selector in the OVERDRIVE position.
2. Accelerate the vehicle to 64-88 km/h (40-55 mph) in FOURTH gear.
3. Quickly increase throttle angle to greater than 50 percent.
4. Verify the following: The TCC releases The transmission downshifts immediately to THIRD gear

Full Throttle Detent Downshift

1. Place the gear selector in the OVERDRIVE position.
2. Accelerate the vehicle to speeds of 64-88 km/h (40-55 mph) in FOURTH gear.
3. Quickly increase throttle angle to 100 percent (WOT).
4. Verify the following: The TCC releases The transmission downshifts immediately to SECOND 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 gear selector in the OVERDRIVE position.
2. Accelerate the vehicle to 64-88 km/h (40-55 mph) in FOURTH gear.
3. Release the throttle while moving the gear selector to THIRD.
4. Verify the following: The transmission downshifts immediately to THIRD gear The engine slows the vehicle

Manual 4-2 Downshift

1. Place the gear selector in the OVERDRIVE position.
2. Accelerate the vehicle to 64-72 km/h (40-45 mph).
3. Release the throttle while moving the gear selector to SECOND.
4. Verify the following: The TCC releases The transmission downshifts immediately to SECOND gear The engine slows the vehicle

Manual 4-1 Downshift

1. Place the gear selector in the OVERDRIVE position.
2. Accelerate the vehicle to 64 km/h (40 mph).
3. Release the throttle while moving the gear selector to FIRST.
4. Verify the following: The TCC releases The transmission immediately downshifts to FIRST Gear. The engine slows the vehicle.

Coasting Downshifts

1. Place the gear selector in the OVERDRIVE position.
2. Accelerate the vehicle to FOURTH gear with the TCC applied.
3. Release the throttle and lightly apply the brakes.
4. Verify the following: The TCC releases Downshifts occur at speeds shown in the Shift Speed table. Refer to Shift Speed, See «Shift Speed»(ref-180352-S04296209532005092800000) .

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.

Reverse

1. With the vehicle stopped, move the gear selector 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 gear selector to FIRST.
2. Accelerate the vehicle to 32 km/h (20 mph).
3. Verify the following: No upshifts occur. The TCC does not apply. There is no noticeable slip, noise, or vibration.

Manual Second

1. With the vehicle stopped, move the gear selector to SECOND.
2. Accelerate the vehicle to 57 km/h (35 mph).
3. Verify the following: The 1-2 shift occurs. The 2-3 shift does not occur. There is no noticeable slip, noise, or vibration.

Manual Third

1. With the vehicle stopped, move the gear selector to THIRD.
2. Accelerate the vehicle to 64 km/h (40 mph).
3. Verify the following: The 1-2 shift occurs. The 2-3 shift occurs. There is no noticeable slip, noise, or vibration.

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 50-55 km/h (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 First 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

Important: 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 in order 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 the 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.

Composition Plates

Dry the plates and inspect the plates for the following conditions

1. Pitting
2. Flaking
3. Wear
4. Glazing
5. Cracking
6. Charring
7. Chips or metal particles embedded in the lining

Replace a composition plate which shows any of these conditions.

Steel Plates

Wipe the plates dry and check the plates for heat discoloration. If the surfaces are smooth, even if color smear is indicated, you can reuse the plate. If the plate is discolored with heat spots or if the surface is scuffed, replace the plate.

Causes of Burned Clutch Plates

The following conditions can result in a burned clutch plate

1. Incorrect usage of clutch plates
2. Engine coolant in the transmission fluid
3. A cracked clutch piston
4. Damaged or missing seals
5. Low line pressure
6. Valve body conditions The valve body face is not flat. Porosity is between channels. The valve bushing clips are improperly installed. The checkballs are misplaced.
7. The Teflon® seal rings are worn or damaged.

Engine Coolant in Transmission

Note. The antifreeze will deteriorate the Viton O-ring seals and the glue that bonds the clutch material to the pressure plate. Both conditions may cause damage to the transmission.

If the transmission oil cooler has developed a leak allowing engine coolant to enter the transmission, perform the following

1. Disassemble the transmission.
2. Replace all of the rubber type seals. The coolant will attack the seal material which will cause leakage.
3. Replace the composition-faced clutch plate assemblies. The facing material may separate from the steel center portion.
4. Replace all of the nylon parts - washers.
5. Replace the torque converter.
6. Thoroughly clean and rebuild the transmission, using new gaskets and oil filter.
7. Flush the cooler lines after the transmission cooler has been properly repaired or replaced.

General Method

1. Verify that the leak is transmission fluid.
2. Thoroughly clean the suspected leak area.
3. Operate the vehicle for 24 km (15 mi), or until normal operating temperatures are reached.
4. Park the vehicle over clean paper or cardboard.
5. Shut OFF the engine.
6. Look for fluid spots on the paper.
7. Make the necessary repairs.

Powder Method

1. Thoroughly clean the suspected leak area with solvent.
2. Apply an aerosol type powder, such as foot powder, to the suspected leak area.
3. Operate the vehicle for 24 km (15 mi), or until normal operating temperatures are reached.
4. Shut OFF the engine.
5. Inspect the suspected leak area.
6. Trace the leak path through the powder in order to find the source of the leak.
7. Make the necessary repairs.

Dye and Black Light Method

A fluid dye and black light kit is available from various tool manufacturers.

1. Follow the manufacturer's instructions in order to determine the amount of dye to use.
2. Detect the leak with the black light.
3. Make the necessary repairs.

Find the Cause of the Leak

Pinpoint the leak and trace the leak back to the source. You must determine the cause of the leak in order to repair the leak properly. For example, if you replace a gasket, but the sealing flange is bent, the new gasket will not repair the leak. You must also repair the bent flange. Before you attempt to repair a leak, check for the following conditions, and make repairs as necessary

Gaskets

1. Fluid level/pressure is too high
2. Plugged vent or drain-back holes
3. Improperly tightened fasteners
4. Dirty or damaged threads
5. Warped flanges or sealing surface
6. Scratches, burrs, or other damage to the sealing surface
7. Damaged or worn gasket
8. Cracking or porosity of the component
9. Improper sealant used, where applicable
10. Incorrect gasket

Seals

1. Fluid level/pressure is too high
2. Plugged vent or drain-back holes
3. Damaged seal bore
4. Damaged or worn seal
5. Improper installation
6. Cracks in component
7. Manual or output shaft surface is scratched, nicked, or damaged
8. Loose or worn bearing causing excess seal wear

Transmission Oil Pan

1. Incorrectly tightened oil pan bolts
2. Improperly installed or damaged oil pan gasket
3. Damaged oil pan or mounting face
4. Incorrect oil pan gasket

Case Leak

1. Damaged or missing fill tube seal
2. Mislocated fill tube bracket
3. Damaged vehicle speed sensor seal
4. Damaged manual shaft seal
5. Loose or damaged oil cooler connector fittings
6. Worn or damaged propeller shaft oil seal
7. Loose line pressure pipe plug
8. Porous casting

Case Porosity Repair

Some external leaks are caused by case porosity in non-pressurized areas. You can usually repair these leaks with the transmission in the car.

1. Thoroughly clean the area to be repaired with a cleaning solvent. Air dry the area. CAUTION: Epoxy adhesive may cause skin irritations and eye damage. Read and follow all information on the container label as provided by the manufacturer. Using instructions from the manufacturer, mix a sufficient amount of an epoxy to make the repair. While the transmission case is still hot, apply the epoxy. You can use a clean, dry soldering acid brush to clean the area and also to apply the epoxy cement. Make certain that the area to be repaired is fully covered. Allow the epoxy cement to cure for three hours before starting the engine. Repeat the fluid leak diagnosis procedures.

Clean-up

1. Disconnect the water supply hose from the J 35944-A and bleed any remaining air pressure from the flusher tank.
2. Remove the fill cap from the J 35944-A and return any unused flushing solution to its container. Rinse the J 35944-A with water. Do not store the J 35944-A with flushing solution in it.
3. After every third use, clean the J 35944-A as described in the instructions included with the tool.
4. Dispose of any waste water/solution and transmission fluid in accordance with local regulations.

How to Use This Section

This section provides the following information

1. General diagnosis information on transmissions
2. Procedures for diagnosing the Hydra-Matic® transmission

When you diagnose any condition of the Hydra-Matic® transmission, begin with Diagnostic Starting Point. This procedure indicates the proper path of diagnosing the transmission by describing the basic checks. This procedure will then refer you to the locations of specific checks. After you have determined the cause of a condition, refer to Repair Instructions for repair procedures. If the faulty component is not serviceable without removing the transmission from the vehicle, refer to Unit Repair for repair information.

Basic Knowledge

Note. Do not, under any circumstances, attempt to diagnose a powertrain condition without basic knowledge of this powertrain. If you perform diagnostic procedures without this basic knowledge, you may incorrectly diagnose the condition or damage the powertrain components.

You must be familiar with some basic electronics in order to use this section of the service manual. You should also be able to use the following special tools

1. A Digital Multimeter (DMM)
2. A circuit tester
3. Jumper wires or leads
4. A line pressure gauge set

Throttle Positions

Engine Braking: A condition where the engine is used to slow the vehicle by manually downshifting during a zero throttle coastdown.

Full Throttle Detent Downshift: A quick apply of the accelerator pedal to its full travel, forcing a downshift.

Heavy Throttle: Approximately 3/4 of accelerator pedal travel, 75 percent throttle position.

Light Throttle: Approximately 1/4 of accelerator pedal travel, 25 percent throttle position.

Medium Throttle: Approximately 1/2 of accelerator pedal travel, 50 percent throttle position.

Minimum Throttle: The least amount of throttle opening required for an upshift.

Wide Open Throttle (WOT): Full travel of the accelerator pedal, 100 percent throttle position.

Zero Throttle Coastdown: A full release of the accelerator pedal while the vehicle is in motion and in drive range.

Shift Condition Definitions

Bump: A sudden and forceful apply of a clutch or a band.

Chuggle: A bucking or jerking. This condition may be most noticeable when the converter clutch is engaged. It is similar to the feel of towing a trailer.

Delayed: A condition where a shift is expected but does not occur for a period of time. This could be described as a clutch or band engagement that does not occur as quickly as expected during a part throttle or wide open throttle apply of the accelerator, or during manual downshifting to a lower range. This term is also defined as LATE or EXTENDED.

Double Bump - Double Feel: Two sudden and forceful applies of a clutch or a band.

Early: A condition where the shift occurs before the car has reached proper speed. This condition tends to labor the engine after the upshift.

End Bump: A firmer feel at the end of a shift than at the start of the shift. This is also defined as END FEEL or SLIP BUMP.

Firm: A noticeably quick apply of a clutch or band that is considered normal with a medium to heavy throttle. This apply should not be confused with HARSH or ROUGH.

Flare: A quick increase in engine RPM along with a momentary loss of torque. This most generally occurs during a shift. This condition is also defined as SLIPPING.

Harsh - Rough: A more noticeable apply of a clutch or band than FIRM. This condition is considered undesirable at any throttle position.

Hunting: A repeating quick series of upshifts and downshifts that causes a noticeable change in engine RPM, such as a 4-3-4 shift pattern. This condition is also defined as BUSYNESS.

Initial Feel: A distinctly firmer feel at the start of a shift than at the finish of the shift.

Late: A shift that occurs when the engine RPM is higher than normal for a given amount of throttle.

Shudder: A repeating jerking condition similar to CHUGGLE but more severe and rapid. This condition may be most noticeable during certain ranges of vehicle speed.

Slipping: A noticeable increase in engine RPM without a vehicle speed increase. A slip usually occurs during or after initial clutch or band apply.

Soft: A slow, almost unnoticeable clutch or band apply with very little shift feel.

Surge: A repeating engine related condition of acceleration and deceleration that is less intense than CHUGGLE.

Tie-Up: A condition where two opposing clutch and/or bands are attempting to apply at the same time causing the engine to labor with a noticeable loss of engine RPM.

Transmission Adaptive Functions

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 automatic transmission input shaft speed sensor (AT 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 transmission pressure control (PC) solenoid to-increase line pressure for the next, same, upshift under identical conditions. If the time of the upshift was shorter than a calibrated value, then the PCM adjusts the current, to the transmission PC solenoid, to decrease line pressure for the next, same, upshift under identical conditions.

Clearing Transmission Adaptive Pressure (TAP)

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, such as the clutch, band, piston, or servo
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 Indicators and Messages

The following transmission-related indicators and messages may be displayed on the Instrument Panel Cluster (IPC). For a complete listing and description of all vehicle indicators and messages, refer to INDICATOR/WARNING MESSAGE DESCRIPTION AND OPERATION in Instrument Panel, Gages, and Console.

4WD: This indicator illuminates when the PCM detects that 4WD has been requested.

Tow/Haul: This indicator illuminates when the PCM detects that tow/haul mode has been requested.

"Trans Fluid Hot": This message is displayed when the PCM detects a transmission fluid temperature (TFT) equal to or greater than 130°C (266°F) for 5 seconds.

"Trans Hot...Idle Engine": This message is displayed when the PCM detects a transmission fluid temperature (TFT) equal to or greater than 135°C (275°F).

Scheme 1203

The energizes the torque converter clutch pulse width modulated (TCC PWM) solenoid valve, which is located on the transmission valve body. The TCC PWM solenoid valve acts on the TCC apply valve in order to control the torque converter clutch application.

The TCC PWM solenoid valve is pulse width modulated by the PCM. This means that the PCM pulses the solenoid so that the hydraulic pressure against the torque converter clutch modulates. This modulated pressure allows the TCC to slip slightly, thus keeping the TCC balanced just at the point of engagement.

One diagnostic code is associated with the TCC PWM solenoid valve Code P1860, TCC solenoid circuit - electrical, detects a fault in the TCC circuit. While Code P1860 is set, both fourth gear in hot mode and the TCC are inhibited. Shift adapts do not update and the MIL illuminates. Recovery can occur on the next ignition cycle.

Scheme 1204

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 0 amps, high pressure, to 1.1 amps, low pressure. The PC solenoid valve current is periodically pulsed in order to prevent contamination from sticking the pressure regulator valve.

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

Scheme 1205

The 1-2 shift solenoid (SS) 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 SS valve is ON in FIRST and FOURTH gear. When commanded ON, the 1-2 SS valve redirects fluid to act on the 1-2 shift valve.

There are two PCM related diagnostic trouble codes (DTCs) associated with the 1-2 SS valve: P0751 and P0753.

The PCM monitors the 1-2 SS 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.

Scheme 1206

The 2-3 shift solenoid (SS) 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 SS valve is ON in THIRD and FOURTH gear. When commanded ON, the 2-3 SS valve redirects fluid to act on the 2-3 shift valve.

There are two PCM related diagnostic trouble codes (DTCs) associated with the 2-3 SS valve: P0756 and P0758.

The PCM monitors the 2-3 SS 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.

Scheme 1207

A gear range sensing device call an automatic transmission fluid pressure (TFP) manual valve position switch assembly is used by the PCM in order to sense which gear range has been selected by the vehicle operator. The TFP manual valve position switch assembly is located on the valve body, and consists of five pressure switches combined into one unit. The PCM applies system voltage to the TFP manual valve position switch assembly on three separate wires. These three circuits are either grounded or open, depending on which gear range has been selected, and on which combination of the five switches gave pressure applied to them.

When the vehicle is in PARK, with the key ON and the engine OFF, the normal state of the TFP manual valve position switch assembly will be DRIVE 2. When the key is ON and the engine is running, the normal state of the TFP manual valve position switch assembly is in PARK/NEUTRAL.

There are two possible combinations of the switches within the pressure switch manifold that do not represent an actual gear range. If the PCM detects either of these combinations, then a diagnostic trouble code (DTC) sets.

The PCM TFP DTC P1810 sets when the TFP switch indicates the following

1. An illegal gear range
2. DRIVE4, DRIVE2 or REVERSE position before and after start-up
3. PARK/NEUTRAL with a ratio greater than 1.05
4. REVERSE with ratio indicating outside of REVERSE
5. DRIVE4, DRIVE3, DRIVE2 or DRIVE1 with ratio indicating REVERSE

While DTC P1810 is present, the PCM assumes DRIVE4 for shift pattern, sets line pressure to maximum, freezes shift adapts, and forces TCC ON with 4th gear commanded.

Scheme 1208

Scheme 1209

Both of the automatic transmission input shaft speed (AT ISS) and the automatic transmission output shaft speed (AT OSS) sensors are magnetic induction sensors. The input and the output sensors are accessible from the left hand side of the transmission. The AT ISS sensor is located just forward of center and the AT OSS sensor is located near the rear. A voltage signal is induced in the AT ISS sensor 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.

Scheme 1210

The PCM used speed information from these sensors in order 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

Code P0502 and P0503 set if a fault exists in the AT OSS sensor circuit, and the PCM calculates a default value using the AT ISS sensor values. As long as the fault remains, and the code 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.

Scheme 1211

The automatic transmission fluid temperature (TFT) sensor assembly is a thermistor which is mounted in the wiring harness assembly. Low transmission temperature produces high resistance, while high temperature produces low resistance. The PCM supplies a 5-volt signal to the TFT sensor assembly through an internal resistor. Then the PCM measures the voltage drop in the circuit. Voltage is high when the transmission is cold and low when the transmission is hot.

The PCM uses the TFT sensor assembly in order to regulate torque converter clutch apply, as well as shift quality.

DTCs P0711, P0712 and P0713 indicate a fault in the TFT Sensor Assembly circuit. After the vehicle has been started, transmission temperature should rise steadily and stabilize between 90-115°C (194-239°F), depending on load. All three DTCs causes the PCM to use a default value of 140°C (284°F), thus reacting as if the transmission were hot in either case. When DTCs P0711, P0712 or P0713 are set, the PCM freezes the shift adapts from being updated, and the MIL illuminates. Some driveability symptoms will be noticed, especially when cold.

Scheme 1212

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 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.

Scheme 1213

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 diagnostic trouble codes 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 reconnection
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. In order 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. In order 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 1214

Scheme 1215

Scheme 1216

Scheme 1217