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DTC codes / B02xx · Airbags, seats, doors, lights and comfort systems / B0237

B0237Backup Lamp Circuit

B0237 indicates a fault in the backup lamp circuit, which is the circuit that powers the reverse lights when the transmission is placed in reverse. The body control module (BCM) or lighting control module monitors this circuit and sets the code when it detects an open, short to ground, short to power, or excessive resistance, meaning the reverse lamps may not illuminate or may stay on constantly.

SystemBody
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaAirbags, seats, doors, lights and comfort systems

Symptoms you may notice

  • Reverse lights do not come on when the gear selector is in reverse
  • Reverse lights stay illuminated at all times, even when not in reverse
  • A warning light on the dashboard, often the check engine light or a dedicated lamp out indicator
  • Often no symptoms besides the warning light, especially if the fault is intermittent
  • Other rear lighting functions (tail, brake, turn) may also be affected if the fault is in a shared ground or connector
  • The backup camera may not activate if it is triggered by the reverse lamp circuit

Common causes, most likely first

  1. Failed reverse lamp switch or transmission range sensor (TRS) on the transmission
  2. Burnt out or incorrect backup lamp bulbs
  3. Corroded, damaged, or disconnected wiring or connectors at the rear lamps or under the vehicle
  4. Blown fuse or faulty relay in the backup lamp circuit
  5. Faulty body control module (BCM) or lighting control module
  6. Short to ground or short to power in the wiring harness between the switch and the lamps

How to diagnose and fix it

  1. Verify the reverse lamps actually operate when the gear selector is moved to reverse, using a helper or a mirror
  2. Check the backup lamp fuse and relay, replacing any blown fuse or faulty relay
  3. Inspect the backup lamp bulbs and sockets for corrosion, damage, or incorrect bulbs
  4. Test the reverse lamp switch or transmission range sensor with a multimeter for continuity and correct operation
  5. Check wiring and connectors from the switch to the lamps for continuity, shorts, and corrosion, repairing as needed
  6. Clear the code and test the circuit; if the code returns, perform a voltage drop test on the ground and power sides
  7. If all external circuits test good, diagnose the BCM or lighting control module for internal faults

What the backup lamp circuit code hides

  • A common misdiagnosis is replacing the BCM when the real problem is a chafed wire in the trunk hinge or a corroded ground behind a rear trim panel.
  • The reverse lamp switch is often integrated into the transmission range sensor, so a faulty sensor can set B0237 without any obvious transmission symptoms.
  • Some vehicles use a separate backup lamp relay controlled by the BCM; a failing relay can cause intermittent operation that sets the code only when the lamps are commanded on.
  • Aftermarket LED backup bulbs can draw too little current and trigger a bulb-out detection circuit, setting B0237 even though the lamps work.
  • The backup lamp circuit often shares a ground with the tail lamps; a bad ground can cause both reverse lamps to be dim or inoperative and set multiple lighting codes.

Can I keep driving with B0237?

The vehicle remains safe to drive because the backup lamps are not a primary safety system, but you should avoid relying on them for visibility when reversing in low light. Have the fault repaired soon to ensure other drivers can see you when you back up and to prevent related lighting issues.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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