OBD-II trouble code
P0374: Timing Reference High Resolution Signal 'A' No Pulses
Nothing at all is arriving on the fine timing reference. It usually means a no-start — and counterintuitively, that makes it the easiest code in this family to diagnose.
Quick facts
- System
- Powertrain
- Category
- Sensors / Timing
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $100 – $1,400
- DIY difficulty
- Intermediate DIY
What does P0374 mean?
P0374 is the hard-failure member of the high-resolution timing family. The other pulse-count codes describe a signal that is present but wrong; this one describes silence. The module looked for the fine timing reference, found nothing whatsoever, and stored the fact.
That brings a practical consequence that shapes everything about the job. Total absence of the reference generally means the vehicle will not start, or will stall and refuse to restart. So unlike its siblings, this fault does not usually arrive under its own power — it arrives on a flatbed, or the owner phones from a car park. Nobody gets to road-test it, and nobody gets to scope a running engine.
The good news is genuinely good, and it is worth stating because it is the opposite of what people expect from a dead car. A fault that is permanently present is far easier to find than one that is not. Everything an intermittent code makes impossible — measure it, wiggle it, prove it — is straightforward here, because the failure will still be failing in an hour. P0374 is the member of this family least likely to end in a guess.
The order of work follows from that. A signal line needs three things to produce pulses: a supply to power the sensor, a ground for it to reference, and an intact path back to the module. Confirm supply at the sensor connector with the ignition on, confirm ground with a voltage drop rather than a continuity beep, and if both are healthy then the signal path or the sensor itself is the only remaining candidate. Three measurements, taken at the sensor rather than at the module, cover the whole circuit.
Cause-wise, total silence points at a shortlist rather than a spectrum. A connector that was unplugged and never reconnected is far and away the most common finding after any work in that area, and it costs nothing to check first. Beyond that: a severed or crushed wire, a sensor with a physically broken tip after a reluctor has spun or contacted it, a blown fuse feeding a shared reference supply, and on optical distributor systems a disc so heavily contaminated with oil that no light passes at all. That last one is worth remembering because the electronics test perfectly while producing nothing.
One reading is worth more than the rest. If other sensors on the same feed have also stored codes, the fault is one supply, not several failed components. Check what else is stored before condemning anything.
Common causes
- Sensor connector left unplugged, partially seated or damaged after recent work in the area
- Severed, crushed or pulled-apart wire in the signal circuit
- Complete internal failure of the sensor with an open winding or dead output stage
- Physically broken or sheared sensor tip after contact with the reference wheel
- Blown fuse or failed relay feeding a supply shared by several reference sensors
- Heavily oil-contaminated optical disc in a distributor pickup blocking the light path entirely
- Reference wheel that has sheared, spun on its hub or lost its teeth
- Failed output driver in the module that generates or conditions the reference on systems where one does
Symptoms
- Engine cranks normally but will not start
- Engine stalls without warning and refuses to restart
- No tachometer movement at all while cranking
- Check engine light on, with the light often coming on before the vehicle finally quits
- No spark, no injector pulse, or both, depending on the strategy
- Multiple related timing or sensor codes stored together when a shared supply is at fault
Diagnostic steps
- 1.Read every stored code before touching the circuit. Several sensors reporting at once is the signature of one failed supply or ground, and it saves an afternoon of testing a healthy sensor.
- 2.Ask what work was carried out most recently. A disconnected or half-seated connector left behind after another repair is the single most common cause of a signal that is completely absent.
- 3.Check the fuse and any relay feeding the reference supply before anything else. It is a two-minute test that occasionally ends the job outright.
- 4.Confirm supply voltage at the sensor's own connector with the ignition on, so the wiring between module and sensor is inside the test rather than outside it.
- 5.Test the ground leg with a voltage drop measurement while the circuit is loaded. A continuity beep passes through a connection that cannot carry current.
- 6.Scope the signal line while cranking. Any activity at all disproves a total open and moves the diagnosis back towards the pulse-count codes.
- 7.Remove the sensor and inspect the tip physically. A sheared or ground-away nose tells you the reference wheel has been in contact with it and that there is a second problem to find.
- 8.On optical distributor systems, open the unit and inspect the disc and optics. A film of oil from a leaking shaft seal blocks the light path completely while every electrical test passes.
- 9.Avoid repeated extended cranking while testing. On some systems that loads cylinders with fuel and creates a second problem on top of the first.
Repair cost
$100 – $1,400
Reconnecting a connector or replacing a fuse can be a $100 to $150 diagnostic charge and nothing else. A replacement sensor is $40 to $200 in parts and $150 to $450 fitted. A severed or crushed wire repaired properly is $150 to $450 depending on how buried the damage is. An optical distributor pickup is usually sold only as a complete distributor, so $350 to $900 with fitting and timing. A module output driver failure means module replacement and programming at $600 to $1,400. Add towing to whichever of those applies, because this code generally leaves the vehicle where it stopped.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with crankshaft position sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.