OBD-II trouble code
P0371: Timing Reference High Resolution Signal 'A' Too Many Pulses
The module counted more timing pulses per revolution than the engine can physically produce. Extra pulses have to come from somewhere, and the sensor is usually not the somewhere.
Quick facts
- System
- Powertrain
- Category
- Sensors / Timing
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $0 – $900
- DIY difficulty
- Intermediate DIY
What does P0371 mean?
Every high-resolution timing reference has a fixed pulse count per crankshaft revolution, and the module knows what that number is. P0371 sets when the count comes back too high. That single word — too many — is what makes this code different from the rest of its family, because a fault that adds pulses is an additive fault, and there are only three ways to add something to a pulse train.
The first is that something electrical is putting extra edges on the wire. The second is that something physical on the reference wheel is being read as a tooth when it is not one. The third is that the counting electronics are seeing one real edge twice. Notice what is not on that list: a failed sensor. A dying pickup produces a weak or missing signal, not a surplus one. That is why P0371 is the member of this family where replacing the sensor first is the least likely repair to work, and it is worth resisting the urge.
The mechanical route deserves attention first because it is cheap to check and disproportionately common. Most high-resolution pickups are magnetic, which means the sensor tip is a small magnet living a few millimetres from a spinning steel wheel. Iron filings and machining swarf migrate to that magnet and stick there, and a clump of debris shaped roughly like a tooth is, from the sensor's point of view, a tooth. This is why extra-pulse codes cluster after engine work — a rebuild, a clutch or flywheel job, a resurfaced flexplate, anything that cut or ground ferrous metal in the neighbourhood. Pulling the sensor and looking at its tip takes minutes and settles the question.
The electrical route is the other big one, and it makes P0371 the code where aftermarket accessories are a legitimate first question rather than a distraction. A high-resolution signal carries many times more edges per revolution than the coarse reference, which means its edges are closer together and a coupled noise spike has an easier time being counted as one of them. Remote starters and alarms spliced into engine-bay wiring, ignition upgrades with unsuppressed leads, badly grounded amplifiers and cheap lighting ballasts all radiate at exactly the wrong frequencies. So does a failing alternator putting AC ripple onto the charging system. A broken or disconnected shield ground on the signal cable removes the one defence the circuit had.
The practical upshot is that P0371 has an unusually wide cost spread. It is the code in this family most likely to end with a parts bill of nothing at all — wipe the sensor tip, reconnect a shield, unplug an accessory — and simultaneously the one where a good sensor is most often thrown away for no benefit.
Common causes
- Ferrous debris or machining swarf collected on the tip of a magnetic pickup and read as an extra tooth
- Electrical noise coupled onto the signal wire from an aftermarket alarm, remote starter, amplifier or lighting kit
- Broken, disconnected or corroded cable shield ground leaving the signal unprotected from interference
- Failing alternator putting AC ripple onto the charging system and onto sensor references with it
- Unsuppressed ignition leads or a spark leak arcing near the timing reference harness
- Damaged reference wheel with a burr, raised edge or repair weld that the sensor counts as an additional tooth
- Chafed signal wire intermittently touching a nearby switched circuit and injecting edges
- Failed signal-conditioning circuitry in the module that receives and counts the pulses
Symptoms
- Check engine light on, sometimes with no obvious change in how the engine runs
- Erratic or impossibly high tachometer readings, or a needle that jumps
- Rough running, stumbling or bucking that comes and goes with electrical load
- Misfire codes recorded when no genuine misfire is happening
- Hesitation on acceleration and reduced power as the module falls back on a protected strategy
- Stalling, or the engine cutting out when a particular accessory is switched on
Diagnostic steps
- 1.Ask what was recently done to the vehicle before touching anything. Engine, clutch, flywheel and flexplate work that cut ferrous metal near the reference wheel is the single strongest lead this code offers.
- 2.Ask what has recently been fitted to the vehicle. An alarm, remote starter, stereo amplifier, lighting conversion or tuning module installed shortly before the code appeared is a suspect, not a coincidence.
- 3.Remove the sensor and inspect its tip under good light. A magnetic pickup holds iron filings, and a clump of them is indistinguishable from a tooth to the module.
- 4.Scope the signal line with the key on and the engine stationary. Any activity at all on a line that should be silent proves the extra edges are electrical and eliminates the reference wheel entirely.
- 5.If the line is quiet with the engine stopped, crank the engine by hand and count pulses over one full revolution against the specification for that engine. This separates a wheel defect from a running-only noise problem.
- 6.Reproduce the fault while switching accessories on and off one at a time with the scope connected. Noise that appears with a specific load names its own source.
- 7.Test the alternator for AC ripple. A shorted diode is a whole-vehicle noise source that will chase you around the engine bay if you do not rule it out.
- 8.Locate the signal cable shield and confirm it is intact and grounded at one end only. A shield grounded at both ends or at neither is a cause rather than a detail.
- 9.Inspect the reference wheel itself for burrs, raised metal and impact damage before concluding the fault is electrical after all.
Repair cost
$0 – $900
This is the one code in its family that can cost nothing to fix. Cleaning debris from a sensor tip, reseating a connector, reconnecting a shield ground or removing an offending accessory are all zero-parts repairs, and diagnostic time of $100 to $180 may be the whole bill. A replacement sensor runs $40 to $200 in parts and $150 to $450 fitted. Noise tracing is the expensive middle ground because it is labour with no part attached, commonly $150 to $400. An alternator replaced for ripple is $350 to $800. Damage to the reference wheel is the worst case and gets expensive fast because of access rather than parts.
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.