Wiper Hi/Lo Relay Coil Short to Ground
The B1437 code indicates a short-to-ground fault in the wiper high/low speed relay coil circuit, specific to Toyota/Lexus vehicles. The Body Control Module (BCM) or multiplex network module detects abnormal continuity to ground in the circuit controlling the relay coil that switches between high and low wiper speeds. This relay is part of the wiper motor control system, enabling speed selection by energizing different motor windings.
1. Commonly Affected Makes
2. Most Common Causes
- Internal short circuit in the wiper hi/lo relay coil
- Damaged insulation or short to ground in wiring between BCM and relay
- Corroded or damaged relay connector pins causing a short to ground
- Internal BCM failure in the relay driver circuit
- Aftermarket electrical modifications causing a ground path
3. Symptoms You Will Notice
- Wipers operate only at one speed or not at all
- Wipers may run continuously without stopping
- Blown fuse for the wiper system
4. Step-by-Step Diagnosis
Scan for codes and verify B1437 is present
Inspect wiper hi/lo relay and its connector for corrosion or damage
Test relay coil resistance and check for short to ground
Check wiring between BCM and relay for shorts or chafing
If wiring and relay are OK, test BCM output or replace BCM
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, but wiper function may be limited or inoperative, which is unsafe in rain. Repair promptly.
How much does it cost to fix?▼
Typically $100–$300 for relay and wiring repair; BCM replacement can exceed $500.