B1991

Pedal Forward / Rearward Potentiometer Feedback Circuit Short to Battery

Body Speed/Idle Control Pedal Position Sensor 🟢 Low — Fix at next service ✅ Safe to Drive
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What This Actually Means

In plain language — no jargon

The pedal position sensor is sending a voltage signal that's stuck at battery voltage (too high), like a light switch that's permanently jammed in the on position. This prevents the engine computer from knowing where the accelerator pedal actually is.

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Symptoms You May Notice

3 known symptoms for this code
Check Engine Light illuminated
Erratic or fixed engine idle speed
Reduced throttle response or limp mode activation
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECM monitors the pedal potentiometer output voltage, which should vary smoothly between 0.5V and 4.5V as the driver moves the accelerator. A short to battery voltage pins the signal at maximum voltage (~12V), preventing normal throttle control and triggering a fault when the voltage exceeds safe thresholds.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Pedal Position Voltage 0.5V to 4.5V (proportional to pedal travel) >5.0V or stuck at battery voltage
Voltage Rate of Change Smooth, gradual transitions Rapid spikes or constant maximum voltage
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Wiring harness connector
Disconnect and inspect the pedal sensor connector for corrosion, water damage, or pushed-back pins; clean with contact cleaner if needed.
2
Pedal assembly wiring
Check for pinched, abraded, or damaged wires between the pedal and ECM that may be shorting to power; repair or replace damaged sections.
3
Accelerator pedal potentiometer
Replace the entire pedal assembly if internal shorts are confirmed and wiring inspection shows no external faults.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1991 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code B1991

What happens after you fix the fault

Once the fault is repaired, B1991 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.