Powertrain, generic (extended)

P23E8 EGR C Flow Excessive Detected

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

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.

Likely causes

EGR valve C held partly open by carbon deposits
Worn valve seat or leaking bypass in path C
Air-mass or EGR flow sensor reading off, so flow is overestimated
Control software needing an update

Symptoms

  • Rough or unstable idle
  • Engine stalls when coming to a stop
  • Hesitation or misfire under load
  • Visible smoke on diesel engines

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–1,200
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

egr valve c

Related codes

P23E7P23E5P23E2P0402P049C

References: law.cornell.edu, gsi.ext.gm.com.