Liftgate Module Replacement - keywords communication defog defogger fob glass HVAC key keyfob learn LGM lock module monitor pressure rear replace rke sensor tire TPM wiper

This PI was superseded to update model years. Please discard PIT4394B.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

There are several conditions which are often diagnosed as the Liftgate Module (LGM) failure.

1. Key Fob does not function properly or it can not be programmed to the LGM.
2. Rear wiper, rear defog, or rear hatch/liftglass lock/unlock does not function or function properly.
3. Low tire pressure warning light comes on particularly in colder weather
4. No communication (Tech II) with the LGM.
5. Tire Pressure Monitor (TPM) Learn procedures will not complete properly.

In a study of LGMs returned under warranty, in the majority of cases, no problems were found with the LGMs. However, there are conditions that have been found when LGM replacement or reprogramming is necessary.

For each conditions listed above (in the Condition/Concern section), please follow the appropriate action below.

1. Key Fob does not function properly or it can not be programmed to the LGM. - See document #1857154 on RKE interference. If no interference is found and the Key Fob is still inop, try to program the keyfobs (see doc. # 665615). If an attempt to program keyfobs to the LGM is unsuccessful, try to learn the TPM sensors, if applicable (see doc. # 1876932). If the TPM learn sequence will not let you get past the horn chirp on the left front wheel and the keyfob would not learn, there is a good chance that the LGM has a bad resistor that is dropping out the RF circuit. If both of these conditions exist the LGM should be replaced, flashed with the proper calibration file (using SPS), and learn the keyfobs and TPM sensors learned. A further confirmation of this condition will be that the module has a date code of 120 thru 273 of 2006 (the date code can be viewed under module information for the LGM on the Tech 2). Otherwise, do not replace the LGM.
2. Rear wiper, rear defog, or rear hatch/liftglass lock/unlock does not function or function properly. - In a few cases modules have been found to have improper operating software/ calibration software combinations. This can cause:

•	the rear wiper malfunction

•	rear defog malfunction

•	rear hatch/liftglass lock/unlock malfunction

•	"no communication" with LGM message displayed on Tech 2

•	indication (on the Tech 2) that the keyfob programmed but the keyfob continues not to function

•	tire pressure sensor learn sequence will not give the double horn chirp to initiate the sequence

•	abnormal battery drain

•

If the calibration software number (look under LGM module information in the Tech II) is 10381248 this is the default manufacturer's calibration and will cause the conditions just described. To remedy this condition the proper calibration file must be flashed to the module using the Tech 2 and the Service Programming System (SPS). In some cases there has been a mismatch between the operating software and the calibration software. The condition may be able to be corrected by flashing the proper calibration to the module using the Tech 2 and SPS, If the calibration file that is listed in SPS is the same as the calibration file in the module, the problem is not with the LGM calibration. Do not replace the LGM.

3. Low tire pressure warning light comes on particularly in colder weather. - The TPM warning light illumination usually does not indicate that the LGM is malfunctioning. It may indicate that the Tire load range or tire pressure placard values are not set properly in the LGM. Check that the pressure settings match the placard values of the label on driver's door. The TPM warning light will normally illuminate when the tire pressure sensor sends a value that is 75% of the placard value plus 2 psi. For example, if the placard value is 35 psi then the light will normally go on when the pressure in the tire reaches 28 psi or less. Given that the tire pressure can drop approximately 1 psi for each 10 ° F temperature change, it is normal that the light may go on when starting out on a cold morning. The tire pressure can increase 2-3 psi when driving the vehicle, so the warning light may go out after the vehicle has been driven for a few miles. The tire pressures should be inflated to the placard values when the vehicle has not been driven for a few hours and tires are at the coldest temperature that the vehicle is likely to see in the driving season. If the tires are warm from being driven or the temperature is higher than the seasonal low temperature when inflated then they should be inflated to the placard pressure value but it may be necessary on a colder day to adjust the pressure up to the placard value to avoid the light coming on.
4. No communication (Tech II) with the LGM. - See item 2.
5. Tire Pressure Monitor (TPM) Learn procedures will not complete properly. - A low battery condition on the J-46079 Tire Pressure Monitor Diagnostic Tool (used in the TPM learn sequence) may be the cause of not getting the horn chirps at the wheels during the TPM sensor learn sequence. Check the battery life indicator level. If it is low, replace the batteries with a set of 100% Alkaline or rechargeable batteries( please note that: just one carbon battery in the tool, mixed with alkaline batteries, will restrict the current flow enough to cause problems with tool operation). Also, check if the tool has the most updated software. The correct software indicates a March 2006 date when the tool is turned on.This software update also improves the battery life and allows compatibility with rechargeable batteries. If a different J-46079 unit is available, try the procedure with the other tool to ensure that problem is not with the J-46079. In some cases when performing the TPM sensor learn sequence the DTC C0775 will be set in the fault history. This is not an indication that the learn sequence failed, unless the DTC has "failed/current" next to it after completing the procedure. Otherwise the DTC can be cleared and the TPM system functions properly. LGM should not be replaced.

Note: After learning tire pressure sensors, the vehicle must be driven for a short distance in order for the LGM to start receiving the tires pressure values. This can be verified by monitoring the tire pressure on the Tech2.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.