Powertrain, generic (extended)

P25A8 Fuel Mode Select Switch Circuit Intermittent/Erratic

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P25A8 records a fuel mode select switch signal that jumps or drops out briefly instead of staying in a stable state. The module sees transitions it cannot attribute to a real press, often while driving over rough roads, which points to a loose terminal, a cracked solder joint in the switch or a harness rubbing behind the trim. Because a press on GM's bi-fuel systems toggles the fuel even while driving, as GM states for its 2015 Impala, unwanted pulses could trigger needless fuel changes, which is why such glitches are flagged. No manufacturer documents P25A8 publicly. Wiggle tests with live data, checking terminal tension and inspecting any conversion harness are the right sequence. Short dropouts may come and go, and the code may return after clearing.

Likely causes

Loose terminal or poor contact at the switch connector
Cracked solder joint inside the switch
Harness rubbing behind the trim and shorting briefly

Symptoms

  • Occasional unexpected fuel mode changes
  • Switch light flickers
  • Code returns sporadically after clearing

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–300
Time0.5–2.5 h

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

Parts involved

fuel mode switch

Related codes

P25A4P25A5P25A6P25A7

References: static.nhtsa.gov, law.cornell.edu.