P0377: The computer's high-resolution engine timing reference signal B shows too few pulses
Timing reference high resolution signal B shows too few pulses
Severity: Severity not verified — if the car runs badly, have it inspected
The sources read for this code only define it and list possible fault locations; none rates its urgency, so no severity is claimed. Have it diagnosed rather than ignoring it, especially if the engine runs poorly or will not start.
P0377 in short
P0377 is a generic code meaning the engine computer's high-resolution timing reference, signal B, signal B shows too few pulses. TroubleCodes.net lists wiring, the crankshaft or camshaft position sensor and the engine computer as the possible fault locations. Have the wiring and sensors checked.
The Delaware DMV list and TroubleCodes.net both title P0377 as a timing reference high resolution signal B fault: signal B shows too few pulses. The timing reference comes from the engine's crankshaft and camshaft position signals.
TroubleCodes.net lists the possible fault locations as Wiring, CKP/RPM/CMP sensor, ECM. It does not publish a detailed guide for this code, so the checks here are limited to what that list supports.
Which sensor feeds signal A or B differs by maker, so the service information for your vehicle should say where each signal comes from.
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 fault in the timing sensor circuit
Possible — needs testing- Why it ranks here
- Wiring is the first item in the fault locations TroubleCodes.net lists, and it is the cheapest to check.
- What would change this
- Rises if a connector is loose, oily or corroded or a wire is chafed. Falls if the harness and connectors are sound.
Cause 2: Crankshaft or camshaft position sensor
Possible — needs testing- Why it ranks here
- TroubleCodes.net lists the crankshaft, RPM or camshaft position sensor as a fault location.
- What would change this
- Rises if the sensor signal is missing or erratic on a scope with sound wiring. Falls if the signal is clean.
Cause 3: Engine control module
Possible — needs testing- Why it ranks here
- TroubleCodes.net lists the engine control module last among the fault locations, so it is a conclusion after the wiring and sensors are cleared.
- What would change this
- Rises only after wiring, sensors and power and ground are proven good. Falls if any earlier cause is found.
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 sensor codes stored with it.
IfCrankshaft or camshaft sensor codes are stored too
It meansStart with the sensor wiring they share.
IfP0377 is the only code
It meansInspect the wiring and connectors.
Step 2: With the engine off and cool, inspect the crankshaft and camshaft sensor connectors and harness for looseness, oil, corrosion or chafing.
Warning:Keep hands and tools clear of belts, the fan and hot exhaust parts, and do not unplug sensors with the engine running.
IfA loose, oily, corroded or damaged connector or wire is found
It meansRepair that first.
Points to: Wiring or connector fault in the timing sensor circuit
IfWiring looks sound
It meansHave the sensor signal checked with a scope.
Step 3: Have a shop compare the crankshaft and camshaft sensor signals on an oscilloscope while cranking and idling.
Warning:Probing the sensor connectors while the engine cranks or runs risks shorting pins and damaging the engine computer; leave it to a shop with the wiring diagram.
IfA sensor signal is missing, erratic or has the wrong pulse count
It meansThe sensor or its trigger wheel is the likely fault.
IfSignals are clean at the sensor but wrong at the computer
It meansThe wiring is the suspect.
Points to: Wiring or connector fault in the timing sensor circuit
IfSignals are clean at the computer and the code returns
It meansThe engine control module is the remaining suspect.
Symptoms
- Check engine light on
- Engine running poorly or stalling is possible, but the sources do not state symptoms
How to fix
Step 1: With the engine off and cool, check the crankshaft and camshaft sensor connectors and wiring for damage, oil or corrosion before replacing any part.
Parts and cost context
- Crankshaft position sensor:Replace a position sensor only after wiring and the signal are checked, and use the part for your engine. 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 P0377 yet. The causes and tests above apply across vehicles.
Related codes
Sources and review
- 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