P0379

Universal

Timing Reference High Resolution Signal B No Pulses

Definition source: General OBD-II reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
Medium Severity

The engine control system expects a high-resolution timing reference from signal B but is not detecting pulses. This signal helps the system track engine timing and operation. If it is missing, the engine may run poorly, stall, or fail to start; an intermittent fault may cause no noticeable symptoms.

Report an error with this code

⚠️ Before You Begin (Safety First)

If the engine stalls, runs severely poorly, or cannot be relied on to keep running, stop driving when it is safe and arrange a tow. A sudden stall can make the vehicle difficult to control. Avoid touching moving or hot engine parts during checks.

Common Symptoms

  • The engine may crank but not start if the control system cannot obtain the timing information it needs.
  • The engine may stall or run roughly if the signal drops out or becomes intermittent.
  • The warning light may turn on when the control system detects that expected signal pulses are absent.
  • There may be no obvious change in how the vehicle runs if the fault is intermittent or other available information lets the system continue operating.

Common Causes

  • A fault in the component or circuit that produces or carries timing reference signal B may prevent pulses from reaching the engine control system.
  • A loose, damaged, corroded, or contaminated electrical connection may interrupt the signal.
  • Wiring damage, a poor power or ground connection where applicable, or electrical interference may disrupt the signal.
  • A damaged or obstructed signal target may prevent the system from producing a usable pulse pattern.
  • A fault in the receiving control-system circuit is possible and should be considered only after the signal source and wiring are checked.

Diagnostic Steps

  1. Note whether the engine starts, stalls, or runs roughly, and record any other diagnostic codes; this context can help narrow down an intermittent signal problem.
  2. With the engine off and cool, visually inspect accessible wiring and connectors related to the timing reference system for looseness, corrosion, chafing, or visible damage.
  3. Check that accessible connectors are seated securely, following the vehicle's service information and avoiding force on connector locks or wiring.
  4. If the code returns or symptoms persist, arrange proper electrical and signal testing; do not replace a sensor based only on this code.

When to Call a Professional

A technician can check related codes and scan data, inspect the signal B wiring and connections, and test the signal waveform while the fault is present. Comparing the signal with other engine timing information can help distinguish a sensor or circuit problem from an issue with its target or another part of the system. Confirm the cause before replacing parts.

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Commonly Asked Questions

Does P0379 prove that a sensor has failed?

No. It reports that pulses from timing reference signal B were not detected. Wiring, connections, the signal target, or the receiving circuit may also be involved.

Can I keep driving with this code?

That depends on how the engine behaves. If it stalls, runs severely poorly, or may stop unexpectedly, do not continue driving; arrange a tow. If there are no symptoms, get the fault diagnosed promptly because it could become intermittent.

What does “no pulses” mean?

The control system expects a changing electrical signal that represents timing information, but it is not detecting the expected pulse activity from signal B.

What testing helps identify the cause?

Checking related codes and scan data, inspecting the circuit, and measuring the signal waveform can help locate whether the interruption is at the signal source, wiring, target, or receiving circuit. Exact procedures depend on the vehicle.

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