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Home >> Jeep >> 2002 >> Grand Cherokee 4WD Limited V8-4.7L >> Repair and Diagnosis >> Powertrain Management >> Transmission Control Systems >> Testing and Inspection >> Flow of Diagnosis >> Diagnostic Trouble Codes >> DTC Descriptions >> Part 1 of 3
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Part 1 of 3

Name of code: P0604, P0605, P0613(11, 13, 16, 17 or 45) Internal Controller
When monitored: Whenever the key is in the Run or Run/Start position.
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- In fact, this DTC is rarely set due to a TCM error, it is usually set by a poor ground.
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. (check main ground attachment to engine block)
- Relay ground circuit. (check main ground attachment to engine block)
- TCM

Name of code: P1684(12) - Battery was Disconnected (Info Only)
When monitored: Whenever the key is in the Run or Run/Start position.
Set condition: This code is set whenever Transmission Control Module (TCM) is disconnected from battery power (B+) or ground. It will also be set during the DRBIII (R) Quick 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 reinitialization of some parameters.
Transmission Effects: Loss of trouble code data. The Transmission system will default to the Immediate shutdown routine 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 (Fused B+)
- TCM disconnected
- Dead Battery
- Low battery voltage during cranking
- Quick Battery Disconnect by DRBIII (R). or MDS
- Bad TCM ground circuit.

Name of code: P0891(14) - Relay Always On
When monitored: When ignition key is turned from "off" position to "run" position and/or ignition key is turned from "crank" position to "run" position.
Set condition: This code is set if the Transmission Control Module (TCM) senses greater than 3 volts at the Trans Control Relay Output terminal(s) of the TCM prior to the TCM energizing the relay.
Theory of operation: The transmission control relay is used to supply power to the solenoids and pressure switches when the transmission is in normal operating mode. The relay output is fed back to the TCM through pins 16, 17, and 36. It is referred to as "Transmission Control Relay Output". This circuit does not supply power to the TCM, it is only a sense circuit. When the relay is off, no power is supplied to the solenoids and pressure switches, and the transmission is in "limp-in" or "default" mode.
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:
- Short to voltage in the Transmission Solenoid/TRS Assembly (internal into any solenoid control circuit)
- Short to voltage on any solenoid control circuit
- Relay contacts stuck together.
- Short to voltage in Transmission Control Relay output circuit(s).
- Short to voltage in Transmission Relay Control circuit.
- Short to voltage on any pressure switch sense circuit.
- TCM connector problems.
- TCM.

Name of code: P0888(15) - Relay Output Always Off
When monitored: Continuously
Set condition: This code is set when less than 3 volts are present at any transmission control relay output (pins 16,17 or 36) circuits at the Transmission Control Module (TCM) when the TCM is energizing the relay.
Theory of operation: The Transmission Control Relay is used to supply power to the solenoids and pressure switches when the transmission is in normal operating mode. The relay output is fed back to the TCM through pins 16, 17, and 36. It is referred to as "Transmission Control Relay Output". This circuit does not supply power to the TCM, it is only a sense circuit. When the relay is off, no power is supplied to the solenoids and pressure switches, and the transmission is in "limp-in" or "default" mode.

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 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:
- Transmission Control Relay (intermittent relay function caused by oxidized or contaminated relay contacts)
- Short to ground or open circuit in the transmission control relay output circuit(s)
- Short to ground or open circuit in the Transmission Solenoid/TRS assembly
- TCM connector problem
- Relay connector problem
- Relay Ground circuit
- TCM Ground circuit(s)
- TCM

Name of code: P0725(18) - Engine Speed Sensor Circuit
When monitored: Continuously with engine running.
Set condition: This code is set when the engine speed calculated by the Transmission Control Module (TCM) is less than 390 RPM, while the engine speed broadcast by the PCM is greater than 383 RPM. The DTC also sets if the calculated engine speed is greater than 8000 RPM for more that 2.0 seconds. Theory of operation: The TCM uses the crank sensor signal to calculate engine RPM. The TCM uses RPM data from the PCM which is broadcast over the communication bus to determine if the engine is running. The TCM continuously compares calculated engine speed to the engine RPM reported on the bus, by the PCM, so that loss of crankshaft position sensor signal to the TCM will not be misinterpreted as engine not running.
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 Logical Shutdown routine.
Possible causes:
- Open or short in engine speed sensor circuit. (Crank sensor signal)
- TCM connector problems (Crank sensor signal or sensor ground terminals)
- Open or short in sensor ground circuit
- Low engine idle speed
- TCM
- PCM.
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