Powertrain, generic (extended)

P2AA1 Alternative Fuel Return Line Valve Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2AA1 is the opposite electrical case to P2AA0: the valve drive wire sits at too high a voltage, usually because it touches a battery-fed wire. Where the module switches the ground side, as in the ROUSH CleanTech Gen 4 propane system with its relay-module ground, a line stuck at supply level leaves no voltage across the coil, so the valve cannot be energized at all and stays in its rest position. When the module then turns its transistor on, it may also see an overcurrent and shut the stage off. A wire nipped between harness bundles or a coil whose winding has shorted to its supply pin are the usual finds. Public manufacturer documentation for P2AA1 does not exist; CARB requires output circuit faults to be flagged.

Likely causes

Control wire shorted to a battery-fed wire in the harness
Solenoid winding shorted to its supply terminal
Bent or bridged pins in the valve connector
Output stage in the fuel control module shorted internally

Symptoms

  • Malfunction indicator lamp on
  • Return valve cannot be switched and stays in its rest position
  • Poor hot starts or switch to the base fuel

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€40–500
Time0.5–3 h

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

Parts involved

alt fuel return line valvewiring harnessafcm

Related codes

P2A9EP2A9FP2AA0P2AA2

References: roushcleantech.com, law.cornell.edu.