Powertrain, generic (extended)

P2A9B Alternative Fuel Tank Select Valve C Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2A9B is logged when the control circuit of tank select valve C reads below the expected level. Common electrical findings are a lead grounded against the frame, a pinched wire under a tank strap or a coil with internal shorts. What follows depends on how the output is wired: a ground-side driver may now keep valve C switched permanently, while a supply-side driver shuts down and lets the valve drop back. Either way the selection of the third vessel no longer follows the commands. Westport's two-vessel patent ties tank changes to empty-tank detection; with the valve out of control, that change may be skipped or forced. No manufacturer documents P2A9B or its voltage limits. Check the circuit with the valve unplugged first, then with the coil reconnected.

Likely causes

Lead of valve C grounded against the frame or pinched under a tank strap
Internal short in the coil of valve C
Water in the plug of valve C

Symptoms

  • Malfunction lamp on
  • Third tank used constantly or not at all
  • Unexpected tank changes during the drive

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,200
Time1–4 h

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

Parts involved

alt fuel tank select valve cwiring harnessafcm

Related codes

P2A99P2A9AP2A9CP2A93P2A97

References: law.cornell.edu, patents.google.com.