Powertrain, generic (extended)

P25A6 Fuel Mode Select Switch Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P25A6 means the fuel mode select switch signal has fallen below the range the module accepts. On a switch that pulls a reference line towards ground when pressed, this is the signature of a signal wire rubbed through to the body or of moisture bridging the switch contacts; a grounded line could otherwise pass for a button held forever. CARB requires input components to be checked for out-of-range values, which is what this code reports. No manufacturer documents P25A6 publicly, though GM's bi-fuel Impala and 2500HD trucks show where the switch lives: dash panel or centre stack, close to cup holders and accessory wiring. Unlike P25A7, the cause is a path to ground, so isolating the switch from its harness is the first test. Fuel selection by hand is lost.

Likely causes

Switch signal wire chafed to ground behind the dash
Moisture or spilt liquid bridging the switch contacts
Switch shorted internally

Symptoms

  • Fuel mode cannot be changed
  • Vehicle remains in one fuel mode

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–300
Time0.5–2 h

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

Parts involved

fuel mode switch

Related codes

P25A4P25A5P25A7P25A8

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