B1988: APP Forward Switch Circuit High Voltage
The B1988 code indicates that the control module has detected abnormally high voltage on the accelerator pedal forward switch circuit, above the expected threshold, which it interprets as a short to battery positive (B+). This switch is part of the accelerator pedal position (APP) sensor assembly or electronic throttle control (ETC) system, and its function is to detect when the pedal is in the forward or travel position. The short to battery prevents the module from receiving a proper variable voltage signal, affecting pedal position interpretation and potentially limiting electronic throttle control.
1. Commonly Affected Makes
2. Most Common Causes
- Short circuit in the forward switch wiring to the 12V power supply circuit
- Internal damage in the APP sensor with low resistance or internal short
- Corroded, bent, or moisture-damaged accelerator pedal connector causing a short between signal and power terminals
- Faulty electronic throttle control module (ETCM) or PCM with damaged input circuit
- Previous incorrect repair or modification to the pedal harness
3. Symptoms You Will Notice
- Check Engine Light or Service Throttle Soon light illuminated
- Reduced engine power or limp mode
- Poor throttle response or hesitation
- Vehicle may not accelerate properly
4. Step-by-Step Diagnosis
Scan for codes and verify B1988 is present; check for related codes.
Visually inspect the accelerator pedal connector and wiring for damage, corrosion, or shorts.
Measure voltage at the forward switch signal wire with key on; compare to specifications.
Test the APP sensor resistance and continuity per manufacturer procedure.
If wiring and sensor check out, suspect a faulty PCM/ECM.
5. Frequently Asked Questions
Is it safe to drive?▼
No, it is not safe to drive. The vehicle may enter reduced power mode or lose throttle control, increasing the risk of an accident. Have the vehicle towed to a repair shop.
How much does it cost to fix?▼
Repair costs typically range from $150 to $600, depending on whether the issue is a simple wiring repair or requires replacing the accelerator pedal assembly or PCM.