$53 (P0733)

Name of code: $50 (P0736) - Gear Ratio Error in Reverse
$51 (P0731) - Gear Ratio Error in 1st
$52 (P0732) - Gear Ratio Error in 2nd
$53 (P0733) - Gear Ratio Error in 3rd
$54 (P0734) - Gear Ratio Error in 4th
$56 (P0715) - Input Speed Sensor Error
$57 (P0720) - Output Speed Sensor Error
$58 (P1794) - 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(P0736) through 54(P0734) sets if the ratio of the input RPM (Nt) to the output RPM (No) does not match the given gear ratio.
- Code 56(P0715) sets if there is an excessive change in input RPM in any gear
- Code 57(P0720) sets if there is an excessive change in output RPM in any gear
- Code 58(P1794) 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(P0736) through 54(P0734) ).
2) An excessive change in input or output speeds indicating signal intermittency will result in codes 56(P0715) and/or 57(P0720) 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(P1794).

Transmission Effects: If a gear/speed ratio error develops, the appropriate code is set as a one trip failure and the 5 minute MIL timer is started. The MIL will illuminate and the transmission system will go into relay open limp-in mode after 5 minutes of substituted gear operation or if three gear/speed ratio error events occur in a given key start. This allows for intermittent problems to correct themselves without opening the relay. Many different events could occur given the range of failures possible for codes 50(P0736) through 58(P1794). The following are a few examples:

- Codes 51 (P0731) thru 57(P0720), at speeds above 45 MPH - The appropriate code is set, EMCC is aborted and current gear is maintained. If while still traveling above 45, 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. The MIL will illuminate and the transmission system will go into relay open limp-in mode if throttle is applied below 45 MPH or at 22 MPH with closed throttle.
- Codes 51(P0731) thru 57(P0720), at speeds between 22 and 45 MPH - If one of these codes is set between 22 and 45 MPH, the current gear will be maintained until the gear/speed ratio problem corrects itself. If throttle is applied, the trans 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 MIL will illuminate and the transmission system will go into relay open limp-in mode with throttle applied at speeds between 22 and 45 MPH.
- Codes 51 (P0731) thru 57(P0720), at speeds below 22 MPH) - If a gear/speed ratio problem is identified below 22 MPH, the transmission will immediately substitute second gear for the current gear. If 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 MIL will illuminate and the transmission system will go into relay open limp-in mode.

Possible causes:
Code 50(P0736) - Excludes geartrain failures which should be obvious upon disassembly
- If code 35(P1791) is also set, follow diagnostic procedure for code 35(P1791) first
- Valve body - #1 ball check or L-R switch valve sticking (may also set code 51 (P0731)
- Speed sensor or associated wiring (may also set codes 51 (P0731), 56(PO715), or 57(P0720) ).
- Failed or slipping L-R clutch - may have code 51 (P0731)
- L-R seal leakage (Intermittent no drive or reverse)
- Sticky L-R 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 51

Code 51(P0731) - Excludes geartrain failures which should be obvious upon disassembly
- If code 35(P1791) is also set, follow diagnostic procedure for code 35(P1791) first
- Valve body - #1 ball check or L-R switch valve sticking (may also set code 50(P0736) or give no reverse)

- Speed sensor or associated wiring (may also set codes 50(P0736), 56(P0715), or 57(P0720))
- Failed or intermittent slipping UD clutch (may also set 52(P0732), or 53(P0733)
- 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 L-R clutch - may have code 50(PO736)
- L-R seal leakage (Intermittent)
- Sticky L-R accumulator seals (intermittent)

Code 52(P0732) - Excludes geartrain failures which should be obvious upon disassembly
- If code 35(P1791) is also set, follow diagnostic procedure for code 35(P1791) first
- Failed or slipping 2-4 clutch - may also set code 54(P0734)
- 2-4 seal leakage (intermittent)
- Sticky accumulator seals (intermittent)
- Failed or intermittent slipping UD clutch - may also set code 51 (P0731) and/or 53(P0733)
- UD seal leakage (intermittent)
- Worn input clutch hub bushing (hard code at heavy throttle)
- Sticky LID accumulator seals (intermittent)
- Worn reaction shaft support seal rings (hard code at heavy throttle)
- Defective solenoid pack (UD pressure in 4th gear)

Code 53(P0733) - Excludes geartrain failures which should be obvious upon disassembly
- If code 35(P1791) is also set, follow diagnostic procedure for code 35(P1791) first
- Failed or slipping OD clutch - may also set code 54(P0734)
- 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 51(P0731) and/or 52(P0732)
- UD seal leakage (intermittent)
- Worn input clutch hub bushing (hard code at heavy throttle)
- Sticky LID accumulator seals (intermittent)
- Worn reaction shaft support seal rings (hard code at heavy throttle)
- Defective solenoid pack (UD pressure in 4th gear)

Code 54(PO734) - Excludes geartrain failures which should be obvious upon disassembly
- If code 35(P1791) is also set, follow diagnostic procedure for code 35(131791) first
- Failed or slipping OD clutch - may also set code 53(PO733)
- 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 52(PO732)
- 2-4 seal leakage (intermittent)
- Sticky accumulator seals (intermittent)

Codes 56(PO715) and 57(PO720)
- 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 58(P1794)
- Open or shorted speed sensor ground (speed sensor ground is different from chassis ground)
- Open or shorted thermostat wiring to TRS
- Defective TRS - Will also set code NP1799)
- Defective TCM