P23E8 code meaning
EGR C Flow Excessive Detected
Powertrain system Generic code P23xx codes Check engine light
What P23E8 means
P23E8 reports that more exhaust gas passes through the third recirculation path, C, than the module allows for the current operating point – the reverse of P23E7. A valve C that does not seat fully, a leaking bypass or a flow sensor reading too high are the usual explanations. CARB requires the OBD system to recognise EGR flow so high that the system can no longer bring it down to the commanded rate. No manufacturer documents P23E8 publicly. GM's 2011 6.6 L LGH diesel shows the equivalent logic for path A (P0402): actual and desired air mass are compared, and a controller deviation between 0.4 and 1.2 g per revolution between 1150 and 1600 rpm, held for 8 s, sets a Type B fault. Expect rough idle, stalling, misfire or smoke.
P23E8 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 4 hours
- Clears after repairAfter a drive cycle
Symptoms of P23E8
- Rough or unstable idle
- Engine stalls when coming to a stop
- Hesitation or misfire under load
- Visible smoke on diesel engines
Common causes of P23E8
- Most likelyEGR valve C held partly open by carbon deposits
- PossibleWorn valve seat or leaking bypass in path C
- PossibleAir-mass or EGR flow sensor reading off, so flow is overestimated
- Less likelyControl software needing an update
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
EGR valve c
What each part of P23E8 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 3 | Area: ignition system or misfire. |
| E8 | The exact fault in that area. |
What to do next
- Note P23E8 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 P23E8
What does P23E8 mean?
P23E8 means "EGR C Flow Excessive Detected". P23E8 reports that more exhaust gas passes through the third recirculation path, C, than the module allows for the current operating point – the reverse of P23E7. It is a generic code, so it means the same on every make.
Is it safe to drive with P23E8?
Drive gently and only to a workshop. With P23E8 the car can go into limp mode (reduced power) to protect itself.
Will P23E8 fail an emissions test?
Yes, it can. P23E8 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 P23E8 to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P23E8 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.