P0378 code meaning
Timing Reference High Resolution Signal B Intermittent/Erratic Pulses
Powertrain system Generic code P03xx codes Check engine light
What P0378 means
Some diesel systems give the injection control a finely divided angle signal in addition to the normal reference signal – the high resolution signal – for precise injection timing and metering. P0378 means a second high resolution signal, B, delivers pulses with erratic spacing or occasional dropouts; it is checked in the same way as signal A (P0370 ff). No manufacturer with a separate signal B was found – GM's diesels with a high resolution signal (6.5-litre, Duramax LB7) only have signal A, and Ford and GM 2014–2019 do not use the codes. The description therefore follows the J2012 name, the analogy to signal A and CARB's monitoring requirement for crank angle sensors. Typically the engine loses power and runs roughly.
P0378 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0378
- Check engine light on
- Loss of power (limp-home fuelling)
- Rough running, hard starting, smoke
Common causes of P0378
- Most likelySensor faulty or dirty
- PossibleLoose contact or interference in the signal wire
- Less likelySensor disc or tone wheel damaged
- Less likelyEngine module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
High resolution timing sensorInjection pumpSensor wiringEngine control module
What each part of P0378 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 3 | Area: ignition system or misfire. |
| 78 | The exact fault in that area. |
What to do next
- Note P0378 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0378
What does P0378 mean?
P0378 means "Timing Reference High Resolution Signal B Intermittent/Erratic Pulses". Some diesel systems give the injection control a finely divided angle signal in addition to the normal reference signal – the high resolution signal – for precise injection timing and metering. It is a generic code, so it means the same on every make.
Is it safe to drive with P0378?
Drive gently and only to a workshop. With P0378 the car can go into limp mode (reduced power) to protect itself.
Will P0378 fail an emissions test?
Yes, it can. P0378 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0378 to fix?
Difficulty: hard. A typical repair takes 1 to 6 hours of work. This is a job for a workshop.
Will P0378 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.