Part 2 of 2
Name of DTC: P-1799(74) Temperature SensorWhen Monitored: Whenever the Engine is running.
Set condition: The DTC is set if any of the following conditions exist for three consecutive ignition starts:
> The Temperature Sensor voltage is out of range (below 0.07 volts or greater than 4.94 volts)
> If continuous erratic Temperature Sensor voltage is sensed
> The Temperature Sensor temperature stays below 80F for an extended period of time
Theory of Operation: The TCM uses a Temperature Sensor to monitor the transmission's sump temperature. This temperature is used to deter - mine which shift schedule the TCM is to use. If the Temperature Sensor circuit fails to operate properly, the TCM will use the calculated oil temperature routine found in prior model year TCMs. If this occurs for three consecutive ignition starts, the DTC will be set. The TCM will then test the Temperature Sensor circuit after every 35th OBDII warm-up start. If the Temperature Sensor circuit is OK, the Temperature Sensor data is used in place of the Calculated Oil Temperature Routine.
Transmission Effects: If the Temperature Sensor indicates a temperature below 0 F or above 240F at start up, the TCM compares the calculated oil temperature to the indicated oil temperature. If the calculated oil temperature differs significantly from the Temperature Sensor value, the calculated oil temperature will be used for that key start. This DTC does not cause the transmission to go into limp-in mode.
Possible Causes:
> Transmission temperature sensor signal circuit short to ground, short to voltage, or open circuit
> Speed sensor ground circuit short to ground, short to voltage, or open circuit
> Temperature Sensor
> TCM
Name of DTC: P-1738(75) - High Temperature Operation Activated
When Monitored: Whenever the engine is running.
Set Condition: Immediately when the Overheat shift schedule is activated.
Theory of Operation: If the transmission oil temperature rises above 240 F and the overheat shift schedule is activated and the DTC is set. The DTC is an information DTC only and is being set to aid the technician in determining root cause of a customer driveability issue. The DTC is also in - tended to alert the technician to determine if a cooling system malfunction has occurred or if an additional transmission air to oil cooler should be added to the vehicle if the customer regularly drives in a manner that overheats the transmission. Extended operation above 240F will reduce the durability of the transmission and should be avoided. Correcting the cooling system malfunction or installing an additional transmission oil cooler will improve transmission durability especially for customers who operate in city/construction stop and go traffic, tow trailers regularly, drive aggressively in low gear or drive regularly in mountainous areas.
Transmission Effects: Information only DTC. - Overheat shift schedule was activated, no limp-in condition occurs. See description of overheat shift schedule.
Possible Causes:
> Transmission Overfilled with Oil
> Engine cooling fan failure
> Engine thermostat stuck closed
> Radiator corroded or packed with dirt
> Transmission cooler corroded or packed with dirt
> Transmission fan not functioning properly
> Transmission Oil Cooler Plugged
> Customer driving pattern requires additional transmission cooling (See Theory of Operation for typical driving patterns that can cause overheating)
Name Of DTC: P-1739(76) - Power-Up at Speed
When Monitored: When TCM (Transmission Control Module) initially powers-up.
Set Condition: If the TCM powers up and senses a valid forward gear PRNDL DTC and the output RPM is above 800 RPM (approx. 20 MPH) the DTC will be set.
Theory of Operation: If a vehicle loses power to the TCM, the solenoids will go to their respective power off state. Some solenoids are normally vented and some are normally applied in their power off state. The transmission is designed to be in 3rd gear with all of the solenoids in this state. However, if power is restored, the TCM will power-up and normal operation will be restored.
This DTC identifies that power to the TCM was restored when the gear selector was in a "Drive" position while the vehicle was moving at speeds above 20 MPH. This DTC does not indicate a problem with the transmission or TCM, instead, it suggests intermittent problems in the fused ignition switch output, fused B(+), or ground circuits to the TCM. Alternately, if a person performs a rolling restart maneuver, the DTC can be set. Therefore it is critical that this DTC be investigated if the vehicle is experiencing intermittent 3rd gear operation and a subsequent return to normal operation.
Transmission Effects: No limp-in, although the symptom might be described as an intermittent limp-in. The DTC is for information only when trying to diagnosis intermittent 3rd gear operation and a subsequent return to normal operation.
Possible Causes:
> No Problem if vehicle is started in "neutral" at speeds above 20 MPH and shifted quickly to a forward gear position.
> Quick key off then on while driving in any forward gear.
FOR INTERMITTENT 3rd GEAR OPERATION AND THEN A SUBSEQUENT RETURN TO NORMAL OPERATION WITHOUT CYCLING THE IGNITION KEY
> Intermittent Direct Battery (Fused B(+)) connection between TCM (60-way pin 56) and battery
> Intermittent Fused Ignition Switch Output between TCM (60-way pin 11) and ignition switch
> Intermittent Ground to TCM (60 way pins 53 and 57)
Name of DTC: P-1765(80) - Switched Battery
When monitored: Ignition key is turned from "off" position to "run" position and for ignition key is turned from "crank" position to "run" position.
Set condition: This DTC is set if the Transmission Control Module (TCM) senses voltage on any of the pressure switch inputs 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. When the relay is off, no power is supplied and the transmission is in "limp-in" mode. The relay output is fed back to the TCM through pins 16, 17 and 38. It is referred to as "Transmission Control Relay Output".
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 transmission control relay output terminals. After this is verified, the voltage at the 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 will illuminate and the transmission system will default to the Immediate Shutdown routine.
Possible causes:
> Short to battery on one or more pressure switch sense circuits
> TCM connector problems
> Solenoid/TRS connector problems
> TCM
Name of DTC:
P-1784(81) - LR Pressure Switch Circuit
P-1734(82) - 2C Pressure Switch Circuit
P-1781(84) - OD Pressure Switch Circuit
P-1733(88) - 4C Pressure Switch Circuit
P-1732(90) - UD Pressure Switch Circuit
When monitored: Whenever the engine is running.
Set condition: The appropriate DTC's set if one of the pressure switches are open or closed at the wrong time in a given gear (see chart below).
Theory of operation: The Transmission system uses five pressure switches to monitor the fluid pressure in the LR, 2C, 4C, UD, and OD clutch circuits. The pressure switches are continuously monitored for the correct states in each gear as And Ever Transmission Effects: The MIL will illuminate and the transmission system will default to the Immediate shutdown routine.
Possible causes:
> If DTC P-1791(35) is present, perform DTC P-1791(35) diagnostic procedures
> Pressure switch senses an open circuit or short to ground between TCM and solenoid/ TRS assembly
> Pressure switch sense circuit shorted to battery
> Pressure switch
> Loose valve body bolts
> Plugged filter - internal transmission or torque converter failure
> Ball check not seating
> Solenoid malfunction (If set with corresponding Solenoid DTC. Ie: 2C Pressure switch set with 2C solenoid)
> Oil Pump (DTC P-1784(81) only)
> TCM
Name of DTC:
P-1728(A2) - 2C Hydraulic Pressure Test Failure
P-1787(A4) - OD Hydraulic Pressure Test Failure
P-1727(A8) - 4C Hydraulic Pressure Test Failure
P-1726(B0) - UD Hydraulic Pressure Test Failure
When monitored: In any forward gear with engine speed above 1000 RPM shortly after a shift and every minute thereafter.
Set condition: Immediately after a shift into a forward gear, with engine speed above 1000 RPM, the TCM momentarily turns on element pressure to the clutch circuits that do not have pressure to identify that the appropriate pressure switch closes. If the pressure switch does not close it is tested again. If the switch does not close the second time, the appropriate DTC is set.
Theory of operation: The Transmission Control Module (TCM) tests the pressure switches when they are off. The test verifies that the switches are operational (They will close with pressure applied). The TCM verifies that the switch closes when the corresponding element is applied. If a switch fails to close, it is re-tested. If it fails the second test, the DTC is set.
Transmission Effects: The MIL will illuminate and the transmission system will default to the orderly Shutdown routine.
Possible causes:
> Pressure switch sense circuit shorted to battery between TCM and Solenoid/TRS assembly
> Solenoid malfunction (If set with corresponding Solenoid DTC. Ie: 2C Hydraulic Pressure switch set with 2C solenoid)
> Low oil pressure
> Pressure switch
Name of DTC:
P-0750(C1) - LR Solenoid Circuit
P-0755(C2) - 2C Solenoid Circuit
P-0760(C3) - OD Solenoid Circuit
P-0770(C4) - 4C Solenoid Circuit
P-0765(C5) - UD Solenoid Circuit
P-1737(C6) - MS Solenoid Circuit
When monitored: Initially at power-up, then every 10 seconds thereafter. They will also be tested immediately after a gear ratio or pressure switch error is detected.
Set condition: Three consecutive solenoid continuity test failures, or one failure if test is run in response to a gear ratio or pressure switch error.
Theory of operation: Six solenoids are used to control the friction elements (clutches). The continuity of the solenoid circuits are periodically tested. Each inactive solenoid is turned on for a few milliseconds, then off. Each active solenoid is turned off for a few milliseconds, then on. This pulsing of voltage to the solenoid causes an inductive spike that can be sensed by the TCM. If an inductive spike is not sensed by the Transmission Control Module (TCM) during the continuity check, it is tested again. If the test fails three consecutive times, the appropriate DTC is set. If the solenoid test is run in response to a gear ratio or pressure switch error, one failure will result in setting the appropriate DTC.
Transmission Effects: The MIL will illuminate and the transmission system will default to the Immediate Shutdown routine (Section 3.2).
Possible causes:
> Open or shorted solenoid circuit(s) between
> TCM and Solenoid/TRS assembly
> Open ground circuit
> TCM connector problems
> Solenoid/TRS connector problem
> Solenoid/TRS assembly
> TCM
Name of DTC:
P-1720(C8) - Line Pressure Error
P-1722(C9) - Line Pressure Low
P-1724(CB) - Line Pressure High
When monitored: Continuously with engine running.
Set condition: The TCM has an internal error counter for each DTC above. When any of the counters reaches a preset threshold, the appropriate DTC is set.
Theory of operation: Line pressured is controlled by the TCM. It is measured by the Line Pressure Sensor (LPS) and regulation is achieved by changing the duty cycle of the Pressure Control Solenoid (PCS). (0% duty cycle = solenoid off = max line pressure, 100% duty cycle = solenoid on = min line pressure). The TCM calculates the desired line pressure based on inputs from the transmission and engine. The TCM calculates torque input to the transmission and uses it as the primary input to the desired line pressure calculation. This is called Torque Based Line Pressure. In addition, the line pressure is set to a preset level (100 or 120 PSI) during shifts and in Park and Neutral to ensure consistent shift quality. The desired line pressure is continuously being compared to the actual line pressure. If the actual line pressure is consistently higher than the target, the line pressure high DTC P-1724(CB) will be set. If the actual line pressure is consistently lower than the target, the line pressure low DTC P-1722(C9) will be set. If it is consistently out of range, but not consistently high or low, it is considered out of range and the line pressure error DTC P-1720(C8) will be set.
Transmission Effects: The MIL will illuminate. The Transmission system will default to open loop line pressure control resulting in a fixed PCS duty cycle. This duty cycle will change slightly depending on temperature and current gear.
Possible causes:
> Sticking Regulator Valve
> PCS
> Line Pressure Sensor
> Oil pump
> Plugged Filter
> 5V supply circuit to Line Pressure Sensor open (Sensor reading will read a constant value between 85 and 95 PSI)
> TCM
Name of DTC: P-1721(CA) - Line Pressure Sensor Error
When monitored: Continuously with engine running.
Set condition: If the Line Pressure Sensor (LPS) voltage is below 0.2 volts or above 4.75 volts the DTC will be set.
Theory of operation: Line pressured is con - trolled by the TCM. It is measured by the LPS and regulation is achieved by changing the duty cycle of the Pressure Control Solenoid (PCS) (0% duty cycle = solenoid off = max line pressure, 100% duty cycle = solenoid on = min line pressure). This sensor is continuously checked for out of range voltage by the TCM.
Transmission Effects: The MIL will illuminate. The Transmission system will default to open loop line pressure control resulting in a fixed PCS duty cycle. This duty cycle will change slightly depending on temperature and current gear.
Possible causes:
> LPS signal circuit shorted to ground, shorted to voltage, or open
> 5-volt supply circuit shorted to ground, shorted to voltage, or open
> Open sensor ground
> Line Pressure Sensor
List of Transfer Case Control Module (TCCM) Diagnostic Trouble Codes (DTC) (Detailed descriptions follow list)
The TCCM may report any of the following DTC's.
If a DTC is Recoverable it may pass and extinguish the 4WD SERVICE Indicator Light in the same ignition cycle in which it has failed earlier. Otherwise, the 4WD SERVICE Indicator Light will remain illuminated until the ignition is cycled.