Part 2A
Name of code: P-0740(38) - Torque Converter Clutch Control CircuitWhen monitored: During Electronically Modulated Converter Clutch (EMCC)
Set condition:
a The transmission must be in EMCC, with the input speed greater than 1750 RPM. The TCC/L-R solenoid must achieve its maximum duty cycle and still not be able to pull the engine speed within 60 RPM of input speed.
b If the transmission is in FEMCC and the engine can slip the TCC by more than 100 RPM (Engine speed-Input speed) for 10 seconds.
The code will be set if one of these event happens three times at a throttle angle less than 30 degrees.
Theory of operation: When in 2nd, 3rd, or 4th gear, the torque converter clutch (TCC) can be locked when certain conditions are met. The TCC piston is electronically modulated by increasing the duty cycle of the L-R/TCC solenoid until the torque converter slip difference (difference between engine and turbine speed) is within 60 RPM. Then the L-R/TCC solenoid is fully energized (FEMCC/100% duty cycle). Torque converter slip is monitored in FEMCC to ensure adequate clutch capacity.
Transmission Effects: EMCC will still be available after code is set. MIL will illuminate after 5 minutes of accumulated slip in FEMCC. The bans will attempt normal operation (no limp-in) even after the MIL is illuminated.
Possible causes:
> Worn pump bushing and/or failed torque converter - both should be replaced during a rebuild with code P-0740(38) present
> Solenoid pack.
Name of code: P-0750(41) - L-R Solenoid Circuit
P-0755(42) - 2-4 Solenoid Circuit
P-0760(43) - OD Solenoid Circuit
P-0765(44) - UD Solenoid Circuit
When monitored: Ignition key is turned from off position to run position and/or ignition key is turned from crank position to run position, then every 10 seconds thereafter, or when a speed ratio or pressure switch error fault is detected.
Set condition: All four solenoids are tested for continuity continuously immediately upon start up and during vehicle operation. For solenoids that are currently energized, power is momentarily interrupted, then reenergized. For solenoids that are not currently energized, the solenoid is momentarily energized, then de-energized. Under both situations, if an inductive spike is not sensed by the Transmission Control Module (TCM) during the continuity check, it is retested twice. If it fails the test the third time, the appropriate code is set.
Theory of operation: Four solenoids are used to control the friction elements (clutches). The continuity of the solenoids circuits are periodically tested. Each solenoid is turned on or off depending on its current state. An inductive spike should be detected by the TCM during this test. If no spike is detected, the circuit is tested again to verify the failure. In addition to the periodic testing, the solenoid circuits are tested if a speed ratio or pressure switch error occurs. In this case, one failure will result in the appropriate code being set. Transmission Effects: The MIL will illuminate and the transmission goes into neutral if code is set above 35 Km/h (22 MPH), limp-in mode when vehicle speed is below 35 Km/h (22 MPH).
Possible causes:
> Open or shorted solenoid circuit(s) between TCM and solenoid pack.
> Open ground circuit.
> TCM connector problems.
> Solenoid pack connector problem.
> Solenoid Pack.
> TCM
Name of code: P-1776(47) - Solenoid Switch Valve (SSV) Latched in L-R Position
When monitored: Continuously when doing partial or full EMCC (PEMCC or FEMCC)
Set condition: If the transmission senses the L-R 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 L-R/TCC solenoid is energized. SSV will be in the downshifted position in 1st gear, thus directing the fluid to the L-R 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 PEMCC or FEMCC, the L-R pressure switch should indicate no pressure if the SSV is in the TCC position. If the L-R pressure switch indicates pressure while in PEMCC or FEMCC, EMCC operation is aborted and inhibited to avoid inadvertent application of the L-R clutch. Partial EMCC will be attempted if the L-R pressure switch does not indicate pressure. A second detection of L-R pressure results in setting the code.
Transmission Effects: At speeds above 45 MPH, EMCC is inhibited. Once speed falls below 45 MPH, the transmission will go into relay open limp-in mode and the MIL will illuminate.
Possible causes:
> Valve body - Solenoid valve stuck in L-R position
> Intermittent short to ground or open circuit in L-R Pressure Switch Sense circuit (with code 24 only)
> Solenoid pack (with code P-1784(24) only)
> TCM (with code P-1784(24) only)
Name of code: P-1793(48) - Torque Reduction (TRD) Link Communication Error
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 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: P-0736(50) - Gear Ratio Error in Reverse
P-0731(51) - Gear Ratio Error in 1st
P-0732(52) - Gear Ratio Error in 2nd
P-0733(53) - Gear Ratio Error in 3rd
P-0734(54) - Gear Ratio Error in 4th
P-0715(56) - Input Speed Sensor Error
P-720(57) - Output Speed Sensor Error
P-1794(58) - Speed Sensor Ground Error
When monitored: The transmission gear/speed ratio is monitored continuously while the transmission is in gear.
Set condition: This code is set if the gear/speed 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/speed 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 indicates an intermittent signal and 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 relay open limp-in mode until three gear/ speed 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/speed 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 relay open limp-in mode if throttle is applied below 72 Km/h (45 MPH) or at 22 MPH with closed throttle.
- Codes 51, 52, 53, 54, 56, and 57 (at speeds between 35 Km/h (22 MPH) and 72 Km (45 MPH) - If one of these codes is set between 35 Km/h (22 MPH) and 72 Km/h (45 MPH), the current gear will be maintained until the gear/speed ratio problem corrects itself. If throttle is applied, the bans will go to 2nd gear. If this happens and the gear/speed ratio problem goes away, normal operation will resume. If three gear/speed 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 relay open limp-in mode with throttle applied at speeds between 35 Km/h (22 MPH) and 72 Km/h (45 MPH).
- Codes 51, 52, 53, 54, 56, and 57 at speeds below 35 Km/h (22 MPH) - If a gear/speed ratio problem is identified below 35 Km/h (22 MPH), the transmission will immediately substitute second gear for the current gear. If a gear/speed ratio problem goes away, normal operation will resume. If three gear/speed ratio problems are identified in a given key start, the transmission will go into relay open limp-in mode.
Possible causes:
Code P-0736(50) - Excludes geartrain failures which should be obvious upon disassembly
> If code P-1791(35) is also set, follow diagnostic procedure for code P-1791(35) first
> Valve body - #1 ball check or LR switch valve sticking - may also set code P-0731(51)
> Speed sensor or associated wiring - may also set codes P-0731(51), P-0715(56), or P-0720(57)
> Failed or slipping LR clutch - may also set code P-0731(51)
- LR seal leakage (Intermittent no drive or re - verse)
- 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 P-0731(51) - Excludes geartrain failures which should be obvious upon disassembly
> If code P-1791(35) is also set, follow diagnostic procedure for code P-1791(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 P-0736(50), P-0715(56), or P-0720(57)
> Failed or intermittent slipping UD clutch - may also set P-0732(52), 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)
> Failed or slipping LR clutch - may also set code P-0736(56) or have no Reverse
- LR seal leakage (Intermittent)
- Sticky LR accumulator seals (Intermittent)
Code P-0732(52) - Excludes geartrain failures which should be obvious upon disassembly
> If code P-1791(35) is also set, follow diagnostic procedure for code P-1791(35) first
> Failed or slipping 2-4 clutch - may also set code P-0734(54)
- 2-4 seat leakage (intermittent)
- Sticky accumulator seals (intermittent)
> Failed or intermittent slipping UD clutch - may also set code P-0731(51) and/or P-0733(53)
> 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 P-0733(53) - Excludes geartrain failures which should be obvious upon disassembly
> If code P-1791(35) is also set, follow diagnostic procedure for code P-1791(35) first
> Failed or slipping OD clutch - may also set code P-0734(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 P-0731(51) and/or P-0732(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)
- Defective solenoid pack (UD pressure in 4th gear)
Code P-0734(54) - Excludes geartrain failures which should be obvious upon disassembly
> If code P-1791(35) is also set, follow diagnostic procedure for code P-1791(35) first
> Failed or slipping OD clutch - may also set code P-0733(53)
- 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 slipping 2-4 clutch - may also set code P-0732(52)
- 2-4 seal leakage (intermittent)
- Sticky accumulator seals (intermittent)
Codes P-0715(56) and P-0720(57)
> Failed input or output speed sensor (intermittent or HARD code)
> Shorted or open wiring between TCM and speed sensor(s) (intermittent)
> Connector problems at 60 TCM connector and/or speed sensor connector
Code P1794(58)
> Open or shorted speed sensor ground (speed sensor ground is different from chassis ground)
> Open or shorted Transmission Temperature Sensor wiring to TRS
> TRS - Will also set code P-1799(74)
> TCM