Set Condition:

Set condition: This code is set whenever Transmission Control Module (TCM) senses an internal error.

Theory of operation: The TCM is constantly monitoring it's internal processor. If an internal problem is detected, this DTC will be set. This DTC can also be set by a bad ground to the TCM and/or Trans Control Relay.

Transmission Effects: The MIL will illuminate (this DTC can take up to five minutes of problem identification before illuminating the MIL) and the transmission system will default to the Immediate Shutdown routine.

Possible causes:

TCM ground circuit.
Relay ground circuit.
TCM

Name of code: P1684(12) - Battery was Disconnected (Informational code Only)

Set condition: This code is set whenever the Transmission Control Module (TCM) is disconnected from battery power (B+) or ground. It will also be set during the DRBIII® Battery Disconnect procedure.

Theory of operation: A battery backed RAM (Random Access Memory) is used to maintain some learned values. When the battery B(+) is disconnected, the memory is lost. When the B(+) is restored, this memory loss is detected by the TCM. The code is set and the learned values are initialized to known constants or previously learned values from EEPROM (Electronic Erasable Programmable Read Only Memory). This results in the initialization of some parameters.

Transmission Effects: Loss of trouble code data. Immediate Limp-in mode if power is lost while operating the vehicle. Normal operation is resumed if the power is restored during the same key start.

Possible causes:

Battery voltage removed from TCM
TCM disconnected
Dead Battery
Low battery voltage during cranking
Battery Disconnect by DRBIII® or MDS
Bad TCM ground circuit.

Name of code: P0891(14) - Transmission Relay Always On

Set condition: This code is set if the Transmission Control Module (TCM) senses greater than 3 volts at the Trans Relay Output (switched battery) terminal of the TCM prior to the TCM energizing the relay.

Theory of operation: The transmission control relay is used to supply power to the solenoid pack when the transmission is in normal operating mode. When the relay is off, no power is supplied to the solenoid pack and the transmission is in Limp-in mode. The relay output is fed back to the TCM through pins 16 and 17. It is referred to as the Trans Relay Output circuit or switched battery.

Transmission Effects: The MIL will illuminate and the transmission system defaults to Logical Limp-in mode. Logical Limp-in mode results in the same modes of operation as Limp-in. Since the relay is stuck "on", the TCM can not open the relay, and the TCM shifts to 2nd gear.

Possible causes:

Relay (welded contacts)
Short to battery in 12-volt supply and/or Transmission Control Relay Output circuit(s)
Short to voltage
TCM connector problems
TCM

Name of code: P0888(15) - Relay Output Always Off

Set condition: This code is set when less than 3 volts are present at the Trans Relay Output (switched battery) terminals at the Transmission Control Module (TCM) when the TCM is energizing the relay.

After a controller reset (ignition key turned to the run position or after cranking engine), the controller energizes the relay. Prior to this the TCM verifies that the contacts are open by checking for no voltage at the switched battery terminals. After the relay is energized, the TCM monitors the terminals to verify that the voltage is greater than 3 volts.

Transmission Effects: The MIL illuminates and the transmission system defaults to Limp-in mode.

Possible causes:

Relay failure (intermittent relay function caused by oxidized or contaminated relay contacts)
Short to ground or open circuit in the Transmission Control Relay circuit(s)
TCM connector problem
TCM

Name of code: P0725(18) - Engine Speed Sensor Circuit

NOTE: This code is not a Transmission input Speed Sensor DTC

Set condition: This code is set when the engine speed sensed by the Transmission Control Module (TCM) is less than 390 RPM or greater than 8000 RPM for more that 2.0 seconds.

Set condition: This code is set if the Transmission Control Module (TCM) senses voltage on any of the pressure switch inputs prior to the TCM energizing the relay.

Immediately after a controller reset (ignition key turned to the run position or after cranking engine), the TCM verifies that the relay contacts are open by checking for no voltage at the switched battery terminals. After this is verified, the voltage at the Solenoid Pack pressure switches is checked. There should be no voltage on the pressure switches at this time. The TCM will then activate the relay.

Transmission Effects: The MIL illuminates and the transmission system defaults to Limp-in mode.

Possible causes:

Short to battery on one or more pressure switch sense circuits
TCM connector problems
TCM

Name of code: P0871(21) - OD Pressure Switch Sense Circuit

Set condition: This code is set if the OD pressure switch is open or closed at the wrong time in a given gear (see chart below).

Theory of operation: The Transmission system uses three pressure switches to monitor the fluid pressure in the LR, 2/4, and OD clutch circuits. The pressure switches are continuously monitored for the correct states in each gear as shown below.