B1989

Pedal Position Rearward Switch Circuit Short to Battery

Body Chassis/Safety Brake pedal switch circuit 🟢 Low — Fix at next service ✅ Safe to Drive
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What This Actually Means

In plain language — no jargon

The brake pedal position sensor is sending a constant high voltage signal to the ECU, as if the wiring is shorted directly to battery power. Think of it like a light switch stuck in the ON position—the ECU can't read the actual pedal movement.

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Symptoms You May Notice

3 known symptoms for this code
Brake warning light illuminated on dashboard
Adaptive cruise control or collision avoidance system disabled
Brake pedal feels normal but electronic systems don't respond properly
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors the brake pedal position rearward switch voltage, expecting it to toggle between low (unpressed) and high (pressed) states. When the circuit shorts to battery, the voltage stays maxed out continuously, preventing the ECU from detecting actual pedal input.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Pedal rearward switch voltage 0.5–4.5V (variable with pedal position) Continuously at 12V or near battery voltage
Signal transition timing Responds within 100ms of pedal movement No voltage change detected; stuck high
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Wiring harness connector at brake pedal switch
Disconnect the pedal switch connector and inspect for corroded or wet terminals; dry and reseat firmly.
2
Brake pedal position switch
Replace the switch if continuity testing shows it remains closed or shorted to power in all positions.
3
Wiring from brake pedal switch to ECU
Inspect the entire harness for pinched, chafed, or melted insulation shorting the signal wire to the positive supply.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1989 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 B1989

What happens after you fix the fault

Once the fault is repaired, B1989 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.