Jeep Cherokee Power Locks
By Greg Montero, AAM
Bus network going down can cause multiple electrical problems.
On Jeep Grand Cherokees 1999-2004, the power door lock system and power window system are operated through the use of a driver door module (DDM) and a passenger door module (PDM). A typical problem found on these vehicles is the programmable communication interface (PCI) bus network goes down, which can cause multiple body electrical problems.
First let’s review PCI bus operation. The PCI bus is a single wire, multiplexed network capable of supporting communication messages shared between modules. Each module provides its own bias and termination, in order to transmit and receive messages. The bus voltage is at zero volts if no modules are transmitting, and then is pulled up to about 7.5 volts when modules are transmitting.
When the bus network goes down, some symptoms you will see include: loss of dashboard gauges, possible power window and power lock problems, multiple ‘bus failure’ fault codes, and failure to communicate with any of the bus modules. The exception is proper communication between the scan tool and the powertrain control module.
It is often discovered, through the bus system diagnostics, that one of the door modules is the cause of the bus network failure. After the door module is identified and replaced, some special items of interest need to be checked. Replacement of the DDM is generally pretty straightforward. However, the PDM requires some additional programming that needs to be performed after replacement; specifically, the key fobs or keyless entry transmitters need to be programmed into the replacement PDM. Use of a compatible scan tool will be required. Currently, the only scan tool that performs this function is the DRBIII.
It would be a good idea to collect all of the customer’s key fobs prior to this programming sequence. Once the passenger door module has been replaced, the steps to program the key fobs include:
1. Main Menu of the DRBIII, select DRBIII Standalone.
2. Select System Page, choose Body Interior.
3. Select Body System page, choose Doors, Gate & Comfort.
4. Doors, Gate & Comfort page, choose Passenger Door.
5. Select Function page, choose Miscellaneous.
6. Select Miscellaneous Function page, choose Program RKE.
7. Program RKE Transmitter page, choose Transmitter #1. Note: Maximum of 4 transmitters can be programmed.
8. Next Program RKE Transmitter page, simply hold down the ‘lock’ or ‘unlock’ button on the key fob to program.
9. Once programming is complete, the screen will indicate a ‘Transmitter Program Successful’ message. You will then be prompted to program any other transmitters.
10. If programming fails for any reason, you will see a ‘Transmitter Reprogram Failed’ message. Try a new battery in the key fob, or the key fob will need to be replaced if it is not transmitting.
Once all the key fobs have been programmed, test each one to verify that the “lock” and “unlock” functions operate normally.
If you have any questions, just give us a call.
Greg Montero, AAM, is the Chrysler team leader. He is a certified ASE Master with L1 certification.
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