B1338

What Does Code B1338 Mean?

DTC B1338 indicates a fault within the Right Rear (RR) Door Ajar circuit, specifically signaling a “Short To Ground” condition. This diagnostic trouble code is typically set by the Body Control Module (BCM) or, in some vehicle architectures, the General Electronic Module (GEM). These control modules are responsible for monitoring the status of all vehicle doors, primarily through door ajar switches, which are usually momentary contact switches integrated into the door latch mechanism. When the RR door is open, the switch completes a circuit, signaling the BCM/GEM; when closed, the circuit is broken or has a different resistance/voltage state. A B1338 code is triggered when the BCM/GEM detects a persistently low voltage signal, characteristic of a short to ground, on the RR door ajar switch input circuit, regardless of the actual physical state of the door (open or closed). This misinterprets the door as being continuously open or “ajar” due to the unintended electrical path to ground.

Common Symptoms

• The Right Rear Door Ajar Warning Light on the instrument cluster remains illuminated constantly.
• The interior dome or courtesy lights stay on even when all doors are confirmed closed, potentially leading to battery drain.
• The vehicle’s security system may malfunction, either failing to arm correctly, generating false alarms, or displaying an “door open” error message upon attempted arming.
• An audible chime or warning tone for an open door may sound persistently while driving or even when parked with the ignition on.
• In some vehicles, functionality related to the affected door, such as specific power window controls or central locking, might be impaired.

What Causes the Code B1338?

• Damaged Wiring Harness: The most prevalent cause is a frayed, pinched, or chafed wire within the Right Rear door jamb, door panel, or leading to the BCM/GEM. This damage causes the signal wire for the door ajar switch to inadvertently contact the vehicle’s chassis or another ground source.
• Faulty Door Ajar Switch: An internal electrical short within the Right Rear door ajar switch itself. The switch may be permanently grounded internally, sending a continuous “ajar” signal to the BCM/GEM regardless of the door’s position.
• Corrosion in Electrical Connectors: Water intrusion, moisture, or environmental contaminants can lead to corrosion within the electrical connectors associated with the Right Rear door ajar switch circuit. This corrosion can create a low-resistance path to ground.
• Improper Aftermarket Accessory Installation: Any recent installation of aftermarket stereo equipment, security systems, or other electronic accessories that involves tapping into or near the door wiring can inadvertently cause a short to ground if not performed correctly.

How to Diagnose and Troubleshoot

Diagnosis of B1338 requires a systematic approach, utilizing a digital multimeter (DMM) and a capable OBD-II scanner:

1. Visual Inspection: Begin by performing a thorough visual inspection of the Right Rear door’s wiring harness, focusing on the area where the harness passes through the door jamb into the body. Look for any visible signs of pinching, fraying, cuts, or corrosion. Examine the door ajar switch itself (often integrated into the door latch assembly) for physical damage or signs of water intrusion. Inspect the connectors at the switch and at the BCM/GEM for corrosion or loose terminals.
2. OBD-II Scanner Data Review: Connect an OBD-II scanner capable of reading live data from the BCM/GEM. Monitor the live data parameter for the “Right Rear Door Ajar Status.” Confirm that the scanner consistently reports the door as “open” or “ajar” even when physically closed. This confirms the BCM/GEM is indeed receiving a faulty signal.
3. Circuit Isolation and Resistance Testing (Harness):
   • Disconnect the electrical connector from the Right Rear door ajar switch.
   • Using a DMM set to resistance (ohms), measure the resistance between the signal wire terminal on the vehicle’s harness side (refer to a vehicle-specific wiring diagram to identify the correct pin) and a known good chassis ground.
   • If a very low resistance (near 0 ohms) is measured, this confirms a short to ground in the wiring harness itself, separate from the switch. The next step is to trace and isolate the damaged section of the wire.
4. Door Ajar Switch Testing (Component):
   • If the harness resistance test was good (infinite or high resistance), the issue likely lies within the switch.
   • With the switch disconnected from the vehicle harness, use the DMM to test the switch’s internal continuity or resistance while manually actuating it (simulating door open/closed states). Refer to service specifications for expected resistance values or continuity states. A faulty switch with an internal short will likely show continuity to ground across its terminals when it should not, or an incorrect resistance reading.
5. Wiggle Test: While monitoring the live data on the OBD-II scanner, or with the DMM connected in voltage mode to the signal wire (back-probed at the BCM/GEM or door jamb connector), gently wiggle, flex, and manipulate the wiring harness in the door jamb, within the door panel, and near the BCM/GEM. A fluctuating voltage reading, or a momentary change in the “Door Ajar Status” on the scanner, strongly indicates an intermittent short caused by damaged wiring that changes state with movement.

Recommended Repairs and Solutions

Once the source of the short to ground has been identified through diagnosis, the appropriate repair can be made:

• Repair Damaged Wiring: If the diagnostic steps indicate a short within the wiring harness, carefully locate the damaged section. Repair any chafed, pinched, or cut wires using appropriate automotive wiring repair techniques, including soldering, heat-shrink tubing, and ensuring proper insulation. Route the repaired wires to prevent future damage.
• Replace Faulty Door Ajar Switch: If the door ajar switch itself is determined to be internally shorted, it will need to be replaced. These switches are often integrated into the door latch assembly, requiring removal of the door panel and potentially the latch mechanism for access. Always use an OEM equivalent or a high-quality aftermarket replacement part.
• Clean and Secure Connectors: If corrosion was found in any electrical connectors, disconnect them, thoroughly clean the terminals with electrical contact cleaner, and apply a thin layer of dielectric grease to prevent future corrosion. Ensure all connectors are securely reattached.
• Address Aftermarket Wiring: If the vehicle has aftermarket accessories that interface with door wiring, inspect these installations carefully for improper wiring or accidental damage that could cause a short. Correct any faulty connections.
• Post-Repair Verification: After performing the repair, use an OBD-II scanner to clear the B1338 diagnostic trouble code. Operate the Right Rear door several times, opening and closing it. Verify that the door ajar warning light extinguishes when the door is closed and illuminates correctly when opened. Drive the vehicle and re-check for the return of the code to ensure the repair is complete and permanent.