What Does B1378 Mean?
This code indicates that the Body Control Module (BCM) has detected a short to ground in the oil change reminder lamp circuit. The BCM monitors the electrical circuit that controls the oil change indicator light on the instrument cluster and has found that voltage is lower than expected, indicating current is flowing directly to ground through an unintended path. This prevents the oil change lamp from functioning properly and may cause it to illuminate continuously or fail to light when needed.
Common Causes
45%
Damaged or chafed wiring harness between BCM and instrument cluster causing short to ground
30%
Failed instrument cluster internal circuitry or LED driver circuit shorted to ground
15%
Corroded or moisture-damaged connector at BCM or instrument cluster pins creating ground fault
10%
Failed Body Control Module internal output driver shorted internally
Diagnostic Steps
1
Step 1: Perform visual inspection of wiring harness between BCM and instrument cluster, focusing on areas near sharp edges, moving components, and heat sources. Look for chafed, melted, or damaged wire insulation that could cause short to ground.
2
Step 2: Disconnect instrument cluster connector and measure resistance from the oil lamp control circuit pin to ground using a digital multimeter. Reading should be infinite or very high (>10k ohms). If low resistance is present, short is in harness; if resistance is high, short is likely in cluster.
3
Step 3: Disconnect BCM connector and measure resistance from BCM side of oil lamp circuit to ground. Should read infinite resistance. Low resistance confirms harness short between BCM and cluster. High resistance suggests BCM internal fault.
4
Step 4: Inspect all connectors in circuit for corrosion, moisture intrusion, bent pins, or contamination. Clean connectors with electrical contact cleaner and apply dielectric grease. Check for pushed-out terminals that may be grounding against connector housing.
5
Step 5: If no wiring faults found, use manufacturer-specific diagnostic software to perform BCM output driver test for oil lamp circuit. Monitor current draw and voltage output during activation to identify BCM or cluster failure.
6
Step 6: After repair, clear codes and monitor oil lamp operation through multiple key cycles and BCM commanded tests to verify proper circuit function and confirm no short remains.
Estimated Repair Cost
$75 - $650
Parts + labor, varies by vehicle and location
This code indicates that the Body Control Module (BCM) has detected a short to ground in the oil change reminder lamp circuit. The BCM monitors the electrical circuit that controls the oil change indicator light on the instrument cluster and has found that voltage is lower than expected, indicating ...
The most common cause of B1378 (Oil Change Lamp Circuit Short To Ground) is: Damaged or chafed wiring harness between BCM and instrument cluster causing short to ground
Typical repair costs for B1378 range from $75 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
This code does not affect vehicle safety or drivability and it is safe to continue driving. The primary concern is loss of the oil change reminder function, which may result in missed oil change intervals if not tracked manually.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1378 to identify the root cause.
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Quick Info
Category
Body
System
Body Control / Instrument Cluster
Difficulty
Type
Manufacturer
Recommended Tools
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