P0398 code meaning
Cylinder 1 Pressure Sensor Circuit High
Powertrain system Generic code P03xx codes Check engine light
What P0398 means
Some diesels have a combustion pressure sensor in the glow plug; the engine module uses it to control injection for each cylinder. This code concerns cylinder 1. P0398 means the sensor signal stays above its upper limit. GM's European 2.0 CDTI diesel (Saab 9-5, 2010) sets it when the signal is above the threshold for more than 2 s with the engine running, checked once per drive cycle, with the check engine light after two trips; the displayed maximum combustion pressure then reads 10,000 kPa instead of the normal 0–9,000 kPa. Saab names a 5 V reference shorted to positive, an open signal wire or one shorted to positive, and an open ground wire as causes – an unplugged connector is the most common. Without the signal, combustion control for this cylinder is switched off, which is usually barely noticeable.
P0398 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P0398
- Check engine light on (often after two trips)
- Usually barely noticeable – combustion control for the cylinder is switched off
- Possibly rougher running, more noise or slightly higher consumption
Common causes of P0398
- Most likelyConnector off or loose, signal wire open
- PossibleSensor ground wire open
- PossibleSensor in the glow plug faulty
- Less likelySignal or reference wire shorted to positive
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Cylinder pressure sensor glow plugSensor wiringEngine control module
What each part of P0398 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. |
| 98 | The exact fault in that area. |
What to do next
- Note P0398 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 P0398
What does P0398 mean?
P0398 means "Cylinder 1 Pressure Sensor Circuit High". Some diesels have a combustion pressure sensor in the glow plug; the engine module uses it to control injection for each cylinder. It is a generic code, so it means the same on every make.
Is it safe to drive with P0398?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0398 fail an emissions test?
Yes, it can. P0398 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 P0398 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P0398 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.