B1629

PRNDL Reverse Input Short To Battery

Body Transmission Control PRNDL Sensor Short 🟢 Low — Fix at next service ✅ Safe to Drive
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What This Actually Means

In plain language — no jargon

The transmission's Reverse gear position sensor is detecting a short circuit to battery voltage, meaning the electrical signal is stuck at maximum instead of varying normally. It's like a light switch that's jammed in the 'on' position—the computer can't read the actual gear selection.

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Symptoms You May Notice

3 known symptoms for this code
Transmission stuck in Limp mode or won't shift into Reverse
Check Engine Light or transmission warning light illuminated
Reverse gear unavailable or erratic transmission behavior
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECM monitors the PRNDL (Park-Reverse-Neutral-Drive-Low) sensor voltage, which should vary between 0–5V depending on gear selection. A short to battery keeps the Reverse input pinned at ~12V when it should be at a specific lower voltage, causing the ECM to recognize an electrical fault rather than a valid gear signal.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Reverse Input Voltage 0.5–2.5V when Reverse selected >10V (shorted to battery)
Signal Continuity <10 ohms to ground Open circuit or short to 12V rail
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
PRNDL sensor connector
Inspect and reseat the connector at the transmission; corrosion or loose pins often cause short-to-battery faults.
2
PRNDL wiring harness
Check for damaged or pinched wires between the sensor and TCM, especially near transmission heat sources.
3
PRNDL sensor assembly
Replace the sensor if wiring and connectors are clean but the fault persists.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1629 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 B1629

What happens after you fix the fault

Once the fault is repaired, B1629 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.