Part 3A

NAME OF CODE: P1776(47) - Solenoid Switch Valve Latched in LR Position

When Monitored: Continuously when doing partial or full EMCC (PEMCC or FEMCC)

Set Condition: If the transmission senses the LR pressure switch closing while performing PEMCC or FEMCC. This code will be set after two unsuccessful attempts to perform PEMCC or FEMCC.

Theory of Operation: The solenoid switch valve (SSV) controls the direction of the transmission fluid when the LR/TCC solenoid is energized. SSV will be in the downshifted position in 1st gear, thus directing the fluid to the LR clutch circuits. In 2nd, 3rd, and 4th, the SSV will be in the upshifted position and directs the fluid into the torque converter clutch (TCC).

When doing PEM CC or FEMCC, the LR pressure switch should indicate no pressure if the SSV is in the TCC position. If the LR pressure switch indicates pressure while in PEMCC or FEMCC, EMCC operation is aborted and inhibited to avoid inadvertent application of the LR clutch. Partial EMCC will be attempted if the LR pressure switch does not indicate pressure. A second detection of LR pressure results in setting the code.

Transmission Effects: At speeds above 72 km/h (45 mph), EMCC is inhibited. Once speed falls below 72 km/h (45 mph), the transmission will go into Limp-in mode and the MIL will illuminate after 5 minutes Of substituted operation.

Possible Causes:
^ Valve body - Solenoid valve stuck in LR position
^ Intermittent short to ground or open circuit in LR Pressure Switch Sense circuit (with code 24 only)
^ Solenoid pack (with code P0841(24) only)
^ TCM (with code P0841(24) only)

NAME OF CODE: P1793(48) - TRD Link Communication Error

NOTE: The MIL will be lit for some engines that limit throttle after a TRD failure

When Monitored: Whenever the engine is running

Set Condition: This code is set when the TCM sends multiple torque reduction messages to the PCM and the TCM does not receive a response from the PCM.

Theory of Operation: During high torque shifts the TCM will send a message requesting that the PCM reduce engine power until the shift is completed. This message is sent from the TCM to the Powertrain Control Module across the Torque Management Request Sense Circuit. The PCM will acknowledge the TCM's request by sending a message across the PCI bus within a specific amount of time. The TRD Link communication is also tested periodically for operation whenever the engine is running and the vehicle is not moving with zero degrees throttle.

Transmission Effects: Maximum throttle angle used by TCM will be 54 degrees. As a result a customer may complain about loss of performance or of short shifting when driving aggressively.

Possible Causes:
^ Sticky Throttle Position Sensor (TPS)
^ Wiring or Connector problems in the Torque Management Request Sense Circuit
^ PCM
^ TCM

NAME OF CODE: P0736(50) - Gear Ratio Error in Reverse
P0731(51) - Gear Ratio Error in 1st
P0732(52) - Gear Ratio Error in 2nd
P0733(53) - Gear Ratio Error in 3rd
P0734(54) - Gear Ratio Error in 4th
P0715(56) - Input Speed Sensor Error
P0720(57) - Output Speed Sensor Error
P1794(58) - Speed Sensor Ground Error

When Monitored: The transmission gear ratio is monitored continuously while the transmission is in gear.

Set Condition: This code is set if the gear ratio is not correct for a period of time.
- Codes 50 through 54 sets if the ratio of the input RPM (Nt) to the output RPM (No) does not match the given gear ratio.
- Code 56 sets if there is an excessive change in input RPM in any gear
- Code 57 sets if there is an excessive change in output RPM in any gear
- Code 58 sets after a TCM reset in neutral and Nt/No equals a ratio of input to output of 2.50

A hard code sets within 3 seconds, an intermittent code sets within 15 seconds.

Theory of Operation: The transmission system uses two speed sensors, one to measure input RPM and one to measure output RPM. These inputs are essential for proper transmission operation. Therefore, the integrity of this data is verified through the following checks:

1) When in gear, if the gear ratio does not compare to a known gear ratio, the corresponding in-gear trouble code is set (codes 50 through 54).
2) An excessive change in input or output speeds indicating signal intermittent will result in codes 56 and/or 57 being set.
3) After a TCM reset in neutral, observing erratic output and input speed sensor signals indicates a loss of the common speed sensors ground. This sets a code 58.

Transmission Effects: The transmission will not go into Limp-in mode until three gear ratio error events occur in a given key start. This allows for intermittent problems to correct themselves without opening the relay. However, if a gear ratio error develops, a code is always set, but if the condition corrects itself the transmission will continue without requiring the ignition key to be cycled on and off. Many different events could occur given the range of failures possible for codes 50 through 58.

The following are a few examples:
- Codes 51, 52, 53, 54, 56, and 57 at speeds above 72 km/h (45 mph) - The appropriate code is set, EMCC is aborted and current gear is maintained. If while still traveling above 72 km/h (45 mph), the gear ratio becomes valid again, EMCC will reengage and normal operation will resume. If the gear ratio becomes intermittent and recovers three times in a given key start, the current gear will be maintained and EMCC inhibited, then the transmission will go into limp-in mode if throttle is applied below 72 km/h (45 mph) or at 35 km/h (22 mph) with closed throttle.
- Codes 51, 52, 53, 54, 56, and 57 at speeds between 35 and 72 km/h (22 and 45 mph) - If one of these codes is set between 35 and 72 km/h (22 and 45 mph), the current gear will be maintained until the gear ratio problem corrects itself. If throttle is applied, the trans will go to 2nd gear. If this happens and the gear ratio problem goes away, normal operation will resume. If three gear ratio problems are identified in a given key start, the current gear will be frozen until throttle is applied. The transmission will then go into Limp-in mode with throttle applied at speeds between 35 and 72 km/h (22 and 45 mph).
- Codes 51, 52, 53, 54, 56, and 57 at speeds below 35 km/h (22 mph). if a gear ratio problem is identified below 35 km/h (22 mph), the transmission will immediately substitute second gear for the current gear. If the gear ratio problem goes away, normal operation will resume. If three gear ratio problems are identified in a given key start, the transmission will go into Limp-in mode.

Possible Causes:
Code P0736(50) - Excludes geartrain failures which should be obvious upon disassembly
^ If code P0944(35) is also set, follow diagnostic procedure for code P0944(35) first
^ Valve body - # 1 ball check or LR switch valve sticking - may also set code P0731(51)
^ Speed sensor or associated wiring - may also set codes P0731(51), P0715(56), or P0720(57)
^ Failed or slipping LR clutch - may also set code P0731(51)
- LR seal leakage (Intermittent no drive or reverse)
- Sticky LR accumulator seals (Intermittent no drive or reverse)
^ Failed reverse clutch (hard code)
- OD/Rev lip seal leakage
- Worn reaction shaft support seal rings
- Snap ring out of position

Code P0731(51) - Excludes geartrain failures which should be obvious upon disassembly
^ If code P0944(35) is also set, follow diagnostic procedure for code P0944(35) first
^ Valve body - # 1 ball check or LR switch valve sticking - may also set code P-0736(56) or have no Reverse
^ Speed sensor or associated wiring - may also set codes P0736(50), P0715(56), or P0720(57)
^ Failed or intermittent slipping UD clutch - may also set P0732(52), or P0733(53)
- UD seal leakage (intermittent)
- Worn input clutch hub bushing (hard code at heavy throttle)
- Sticky UD accumulator seals (intermittent)
- Worn reaction shaft support seal rings (hard code at heavy throttle)
- Solenoid pack (UD pressure in 4th gear
^ Failed or slipping LR clutch - may also set code P0736(56) or have no Reverse
- LR seal leakage (Intermittent)
- Sticky LR accumulator seals (Intermittent)

Code P0732(52) - Excludes geartrain failures which should be obvious upon disassembly
^ If code P0944(35) is also set, follow diagnostic procedure for code P0944(35)
^ Failed or slipping 2-4 clutch - may also set code P0734(54)
- 2-4 seat leakage (intermittent)
- Sticky accumulator seals (intermittent)
^ Failed or intermittent slipping LTD clutch - may also set code P-0731(51) and/or P-0733(53)
- UD seal leakage (intermittent)
- Worn input clutch hub bushing (hard code at heavy throttle)
- Sticky UD accumulator seals (intermittent)
- Worn reaction shaft support seal rings (hard code at heavy throttle)
- Defective solenoid pack (UD pressure in 4th gear)

Code P0733(53) - Excludes geartrain failures which should be obvious upon disassembly
^ If code P0944(35) is also set, follow diagnostic procedure for code P0944(35) first
^ Failed or slipping OD clutch - may also set code P0734(54)
- OD and Reverse inner and outer lip seal leakage (usually hard code)
- Sticky OD accumulator seals (intermittent)
- Worn reaction shaft support seal rings (hard code at heavy throttle)
- Broken OD/UD tapered snap ring - (hard code at heavy throttle)
^ Failed or intermittent slipping UD clutch - may also set code P0731(51) and/or P0732(52)
- UD seal leakage (intermittent)
- Worn input clutch hub bushing (hard code at heavy throttle)
- Sticky UD accumulator seals (intermittent)
- Worn reaction shaft support seal rings (hard code at heavy throttle)
- Solenoid pack (UD pressure in 4th gear)