P2A28

Code

Generic P — Powertrain

Alternative Fuel Tank Shutoff Valve C Control Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 12 EN: 21 RU: 17

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Short to ground in the valve control wire
Open or high-resistance wiring / connector between PCM and valve
Poor or corroded connector or pin at valve or PCM
Failed shutoff valve (open or internally shorted coil)
Blown fuse or faulty relay supplying valve circuit
Faulty PCM/ECM output driver

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
Alternative fuel shutoff valve C does not actuate when commanded
Vehicle may default to backup fuel or disable alternative fuel operation
Possible difficulty starting or rough running when on alternative fuel
Stored DTC related to alternative fuel system control

What to check

Retrieve freeze frame and readiness data; confirm conditions when code set
Visually inspect valve connector, wiring harness, and engine/vehicle grounds for damage, corrosion, or water intrusion
Check related fuses and relays for continuity and correct operation
Backprobe valve control connector; measure voltage with key ON and while commanding valve ON
Measure coil resistance across the valve control pins with connector disconnected
Check continuity from valve control pin to PCM pin and for shorts to ground

Signal parameters

Expected control voltage when commanded ON: ~battery voltage (approx. 11–14.5 V) at the valve control pin
Expected control voltage when commanded OFF: near 0 V (driver to ground) or high-impedance depending on design
Typical coil resistance (manufacturer dependent): commonly 5–50 ohms; check service data for exact value
Expected current draw when energized: typically a fraction of an amp to a few amps depending on valve; confirm with service specs
Monitor waveform for steady DC when energized; excessive drop indicates short/high resistance

Diagnostic algorithm

Verify the code: read DTCs, note freeze-frame and operating conditions, then clear codes and attempt to re-create.
Visual inspection: examine valve connector and harness for damage, corrosion, loose pins, or water intrusion. Repair any obvious issues.
Check power/fuse/relay: verify the supply fuse and any relays powering the valve are good and receiving battery voltage.
Backprobe with key ON, engine OFF: command the valve ON via scan tool and measure voltage at the valve control pin. If voltage is low (
Measure coil resistance: disconnect harness at valve and measure resistance across valve terminals. Compare to spec. Open or very high resistance = faulty valve; near shorted or very low = internal short.
Continuity and short check: with harness disconnected, check continuity from valve control pin to the PCM connector pin and check for shorts to ground. Repair any wiring faults.
Bench-test valve: apply battery voltage to the valve (through an inline fuse and briefly) to verify operation and current draw. If valve operates and draws normal current, suspect wiring/PCM driver.
If wiring and valve OK, test PCM output driver: monitor PCM command while commanding valve ON; if PCM does not provide correct voltage but has proper control signal, consider PCM fault or software/config issue.
After repairs or component replacement, clear codes and perform functional test and road test to confirm repair and that the DTC does not return.

Likely causes

Wiring shorted to ground or poor connector/ground at valve
Failed valve coil (open or internal short)
Blown fuse or bad relay in valve supply circuit
PCM/ECM driver fault (less common)

Fault status

⚠️ Status

Low voltage detected on Alternative Fuel Tank Shutoff Valve C control circuit when commanded ON. Possible wiring short, connector issue, faulty valve coil, blown fuse/relay, or PCM driver fault.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours

Repair manuals