Intermittent door unlock issues can be frustrating on any vehicle, especially on a Jeep Grand Cherokee. This article dives into a specific case involving a Jeep Grand Cherokee with all doors experiencing intermittent unlocking problems, accompanied by a P1009-00 diagnostic trouble code (DTC).
The vehicle presented with all doors failing to unlock intermittently, regardless of the method used: key fob, driver’s side switch, passenger side switch, or capacitive touch handles. A diagnostic scan revealed only one code: P1009-00, indicating an issue with the humidity sensor module. While this code might seem unrelated, it’s important to consider all potential factors. Further diagnostics revealed that the key fob’s unlock signal was being registered by the RF hub, the driver and passenger switches were sending unlock requests to the Body Control Module (BCM), but the BCM wasn’t sending the necessary output signal to activate the door lock actuators. No relay click could be heard, suggesting a lack of signal from the BCM.
The wiring diagram was consulted. The driver’s door switch communicates directly with the BCM via a Local Interconnect Network (LIN) bus. The RF hub uses the Controller Area Network (CAN) bus, and the passenger door switch, a simple resistor-based system, connects to the passenger door module, which then communicates with the BCM over the CAN bus. The BCM is the common denominator in all these systems.
All doors were verified to correctly register open/closed and locked/unlocked statuses. A new BCM was installed, but the problem persisted.
Further testing involved scoping the CAN and LIN buses. With the ignition off and the networks asleep, pressing the unlock button didn’t unlock the doors, but it did wake up both networks. This suggests that the BCM is receiving the unlock request but not acting upon it for an unknown reason.
The main ground at the BCM was amplified with the ignition off to observe any changes in actuator current draw, but no anomalies were detected. Power and ground circuits related to the door locks were thoroughly checked and load tested, revealing no issues. Disconnecting the battery for over an hour didn’t resolve the problem either. All necessary relearns were performed, and the vehicle’s software was updated using a WiTECH diagnostic tool. As a final measure, both door switches were unplugged, yet the issue remained. The root cause of this intermittent door unlock problem, linked to the P1009-00 code in the Jeep Grand Cherokee, remains elusive. Further investigation is needed to pinpoint the underlying issue. Could there be a problem with the CAN or LIN bus communication, despite the networks waking up? Is there a potential software glitch within the BCM, even with the latest updates? Could an external factor, such as interference or a faulty sensor not directly related to the door lock system, be influencing the BCM’s behavior?
