B1657: Driver Rear Seat Up Motor Circuit Short to Battery
Diagnostic trouble code B1657 indicates a short to battery voltage in the control circuit for the driver's rear seat tilt-up motor. This circuit is part of the seat memory module or seat position module, depending on the vehicle configuration. The code sets when the control module detects battery voltage on the motor control circuit when it should not be present, typically due to a short circuit in the wiring or the seat motor itself. This code is specific to Toyota/Lexus vehicles equipped with power memory seats. The system continuously monitors the resistance and voltage of the seat motor circuits; when it detects an out-of-range high voltage for a specified time, it stores the fault code and may disable the seat memory function.
1. Commonly Affected Makes
2. Most Common Causes
- Short circuit in the wiring harness between the seat control module and the rear lift motor
- Damaged seat motor with deteriorated internal insulation causing a short
- Corroded or moisture-contaminated seat motor connector causing a short circuit
- Seat control module (Seat ECU) with a shorted control transistor
- Harness damage from chafing or pinching that exposes conductors
3. Symptoms You Will Notice
- Seat memory function inoperative
- Driver rear seat tilt-up motor does not operate
- Seat position may be stuck or move erratically
- Check engine or seat warning light illuminated
4. Step-by-Step Diagnosis
Scan for codes and verify B1657 is present
Visually inspect the wiring harness and connectors between the seat control module and the rear lift motor for damage, corrosion, or moisture
Disconnect the seat motor connector and measure resistance between motor terminals; compare to specifications
Check for battery voltage on the motor control circuit at the module connector with the motor disconnected; voltage should be near 0V when not commanded
If wiring and motor check out, test the seat control module for internal short by swapping with a known good module or performing module self-test
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is generally safe to drive, but the seat memory function will be disabled and the rear seat tilt adjustment may not work. The issue is moderate severity and should be repaired to restore full seat functionality.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, depending on whether the cause is a wiring repair (lower end) or replacement of the seat motor or control module (higher end). Diagnostic fees may add $100-$150.