Timing Reference High Resolution Signal "B" Intermittent/Erratic Pulses
The P0378 code means the vehicle's onboard diagnostic system has detected: Timing Reference High Resolution Signal "B" Intermittent/Erratic Pulses. This is a critical severity code.
- Keep driving?
- No — stop driving
- DIY difficulty
- hard
- Estimated cost
- $100 - $600 (parts and labor)
Best-selling code reader on Amazon. Reads and clears check engine codes on any 1996+ vehicle. Under $30.
Essential for diagnosing sensor codes, checking voltage, and testing circuits. Under $15 and pays for itself on the first job.
Affiliate links — we earn a commission at no extra cost to you.
What Are the Symptoms of P0378?
- Check Engine Light on
- Intermittent stumbling or stalling
- Symptoms that come and go with heat or rain
- Possible hard starting
What Causes P0378? (Most Likely First)
- Loose, corroded or chafed wiring in the signal circuit High
- Failing sensor that cuts out when hot or wet High
- Electrical interference on the signal wiring Moderate
- Engine computer fault Low
Can I Still Drive with P0378?
No — stop driving. P0378 is rated critical severity. Continuing to drive in this state risks further damage — get it looked at before your next trip.
Frequently Asked Questions
What does P0378 mean?
P0378 means Timing Reference High Resolution Signal "B" Intermittent/Erratic Pulses: this signal is dropping in and out or arriving with irregular spacing.
What is a high-resolution timing reference?
Some engine computers track engine position with two signals: a low-resolution reference for basic timing and a high-resolution signal with many more pulses per revolution for precise spark and fuel timing. Which sensor produces the high-resolution signal depends on the engine.
Is it safe to drive with P0378?
Have it diagnosed before relying on the vehicle. A fault in an engine position signal can cause stalling or a no-start, sometimes without warning.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose P0378?
-
Note any other stored codes. Crankshaft or camshaft position codes alongside this one often share the same wiring or sensor fault.
-
Look up which sensor supplies high-resolution signal "B" on your engine. It differs by manufacturer, so the service information is the reliable source.
-
Inspect that sensor's wiring and connector for chafing, corrosion, moisture or a loose pin.
-
With a scope, compare the high-resolution signal against the low-resolution reference while the engine runs or cranks.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Explore More
Was this helpful?
Send this to whoever is fixing the car — your mechanic, or the person asking what the light means.