P2039 serious

Reductant Injection Air Pressure Sensor Circuit Low

The P2039 code means the vehicle's onboard diagnostic system has detected: Reductant Injection Air Pressure Sensor Circuit Low. This is a serious severity code.

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Keep driving?
Short distances only
DIY difficulty
hard
Estimated cost
$200 - $600 (parts and labor)
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Common Symptoms

  • Check Engine Light on
  • DEF system malfunction indicator
  • Engine power reduction
  • SCR system not functioning
  • Possible speed limiter activation

Probable Causes (Ranked by Likelihood)

  • Short to ground in air pressure sensor circuit Very High
  • Failed air pressure sensor High
  • Water intrusion in sensor connector Moderate
  • Damaged wiring near exhaust heat Moderate
  • PCM input circuit fault Low

Step-by-Step Diagnostic Procedure

  1. Confirm P2039 with freeze frame data

  2. Check air pressure sensor connector for moisture or corrosion

  3. Measure sensor signal voltage at connector

  4. Inspect wiring for shorts to ground

Frequently Asked Questions

What does P2039 mean?

P2039 indicates the reductant injection air pressure sensor circuit is reading below the minimum voltage, usually from a wiring short to ground or sensor failure.

Can I drive with a P2039 code?

Drive only short distances. The SCR system will not function, and some vehicles may activate a speed limiter if not repaired promptly.

How much does it cost to fix P2039?

Repair costs are typically $200 to $600 for sensor or wiring repair.

Sources

This page is built from documented references. Verify against your own service info before repair work.

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