P0378 critical

Timing Reference High Resolution Signal B Frequency Not Within Expected Range

The P0378 code means the vehicle's onboard diagnostic system has detected: Timing Reference High Resolution Signal B Frequency Not Within Expected Range. This is a critical severity code.

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Keep driving?
No -- stop driving
DIY difficulty
hard
Estimated cost
$100 - $600 (parts and labor)
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Common Symptoms

  • Check Engine Light on
  • Engine may run rough or stall
  • Incorrect RPM or cam position readings
  • Ignition timing errors

Probable Causes (Ranked by Likelihood)

  • Faulty camshaft position sensor B producing incorrect frequency Very High
  • Damaged reluctor wheel teeth High
  • Sensor installed at wrong air gap Moderate
  • PCM signal processing fault Low

Step-by-Step Diagnostic Procedure

  1. Compare cam sensor frequency at various RPMs to manufacturer specification.

  2. Check sensor air gap and mounting.

  3. Inspect reluctor wheel teeth.

  4. Replace sensor if frequency is consistently out of range.

Frequently Asked Questions

What is cam sensor frequency?

Frequency is how fast the signal pulses arrive. It should increase proportionally with engine RPM. If it does not, the sensor or reluctor is faulty.

Can a wrong sensor cause P0378?

Yes, installing the wrong part number cam sensor can produce signals at the wrong frequency for that engine.

Is P0378 a PCM problem?

Rarely. While the PCM processes the signal, the fault is almost always in the sensor, reluctor wheel, or sensor installation.

Sources

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

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