P0378: The computer sees erratic or dropping pulses on a second high-resolution engine position signal
Timing reference high resolution signal B intermittent/erratic pulses
Severity: Severity not verified — if the car runs badly, have it inspected
The sources define the code and list causes but do not say how serious it is, so severity is not verified.
P0378 in short
P0378 means the engine computer is getting erratic, intermittent pulses on its high-resolution timing reference signal B, which comes from the engine position sensors. TroubleCodes.net lists wiring or connections, the crankshaft, RPM or camshaft sensor, and the computer as probable causes. Have the sensor circuit tested.
The computer times spark and fuel from pulses that engine position sensors send as the engine turns. P0378 is set when one of those timing reference signals, labelled signal B, arrives intermittently or erratically instead of as a clean, steady train.
Both the Delaware DMV generic code list and TroubleCodes.net give the same meaning. Which sensor is signal B depends on the maker, so the vehicle's service information is needed to identify the circuit. TroubleCodes.net has not published a detailed guide for this code, so the cause list is short.
Most likely causes
These are general causes for this code across vehicles. None is specific to one make or model.
Cause 1: Wiring or connector problem in the timing signal circuit
Possible — needs testing- Why it ranks here
- TroubleCodes.net lists wiring problems and poor electrical connections first, and an erratic signal is the typical result of a loose or damaged connection.
- What would change this
- Rises if the harness or connector shows damage, corrosion or looseness, or wiggling it changes the signal. Falls if the circuit tests clean.
Cause 2: Crankshaft, RPM or camshaft position sensor
Possible — needs testing- Why it ranks here
- TroubleCodes.net names the CKP, RPM or CMP sensor as a probable cause; the sensor producing signal B is identified from the vehicle's manual.
- What would change this
- Rises if the wiring is good and the sensor signal is erratic on an oscilloscope. Falls if the sensor output is steady.
Cause 3: Engine control module
Possible — needs testing- Why it ranks here
- TroubleCodes.net lists the computer, but only after wiring and sensors are cleared.
- What would change this
- Rises only if the wiring and the sensor both test good. Falls if either is faulty.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Read all stored codes and freeze-frame data with a scan tool, and note any crankshaft or camshaft codes stored with P0378.
IfOther crank or cam signal codes are stored
It meansThe shared circuit, sensor or computer may be involved; note them for the shop.
IfOnly P0378 is stored
It meansLook at the wiring and connectors next.
Step 2: Look over the wiring and connectors of the crankshaft and camshaft sensors for damage, corrosion or looseness.
IfDamaged, corroded or loose wiring is found
It meansRepair it and retest.
Points to: Wiring or connector problem in the timing signal circuit
IfWiring looks good
It meansHave the sensor signal checked on a scope.
Step 3: Have a shop watch the crankshaft and camshaft sensor signals on an oscilloscope while the engine is cranked or running and compare them with the manual.
Warning:Probing running or cranking circuits near moving belts and the crank pulley can cause injury, and shorting a sensor circuit can damage the computer. Leave this to a shop.
IfA sensor signal drops out or is erratic
It meansThe sensor is suspect.
IfSensor signals are clean but the code returns
It meansThe computer may be at fault, rare; a shop should confirm.
Symptoms
- Check engine light is on
- Engine may run unevenly or stumble if the timing signal drops out
How to fix
Step 1: With the engine off and cool, look at the visible wiring and connectors near the crankshaft and camshaft sensors for chafing, oil soaking or loose plugs.
Parts and cost context
- Crankshaft position sensor:Confirm the sensor and wiring with a test before buying one. Labour varies; get a quote.
Labor varies by vehicle and shop; get a quote before you approve a repair.
Compare used part prices on PartPriceGuideOn your vehicle
We don't have reviewed vehicle-specific evidence for P0378 yet. The causes and tests above apply across vehicles.
Related codes
No curated relationships for P0378 yet.
P0378 questions
Is it safe to drive with P0378?
Not enough is sourced to say. The code is about the engine position signal that times fuel and spark, so if the engine stumbles or stalls, stop driving it and have it checked.
Sources and review
- TroubleCodes.net P0378: timing reference high resolution signal B intermittent/erratic pulses
- On-Board Diagnostic Trouble Codes (generic code title list)
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error