P0378
Timing Reference High Resolution Signal B Intermittent/Erratic Pulses
Ignition / engine timing
Generic OBD-II
High
What it means
P0378 means the "B" high-resolution timing reference signal is dropping out or producing erratic pulses. The ECM uses this precise signal to time spark and fuel, so intermittent faults can cause misfires, stalling, or an occasional no-start. The usual culprit is the reference sensor, its wiring, or a damaged reluctor ring — and intermittent codes point to wiring first.
High
Can I keep driving? Risky — erratic timing pulses can cause misfires, stalling, or a no-start; drive minimally until the fault is traced.
Common symptoms
What you'll notice
- Check-engine light on
- Engine misfires or runs unevenly
- Stalling or intermittent no-start
- Hesitation and reduced power
Common causes
Most likely first
- Faulty high-resolution timing sensor (optical/crank/cam reference)Likely
- Damaged or chafed wiring causing intermittent signal dropoutCommon
- Loose or corroded connector at the sensorCommon
- Worn or damaged crank/cam reluctor ringsLess often
- ECM fault (rare — confirm sensor and wiring first)Less often
How to diagnose & fix
Work through it in order
- Scan and read freeze-frame data, capturing the conditions when the erratic pulses appear.
- Wiggle-test the sensor connector and harness while watching the signal — intermittent faults are usually wiring.
- Inspect the reference sensor and its reluctor ring for damage, debris, or excessive gap.
- Back-probe the sensor for supply, ground, and a clean pulse pattern while cranking and running.
- Replace the timing-reference sensor if it produces erratic pulses with good wiring. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0378?+
Not really — erratic timing signals can make the engine stall or fail to restart unexpectedly. Have it diagnosed before relying on the vehicle.
Can I just clear P0378?+
Because the fault is intermittent it may stay away briefly, but it returns until the sensor or wiring is repaired.
Related codes
Often seen with P0378
Read & clear P0378 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX