P2A74: Alternative Fuel Hydraulic Fuel Pump Select Valve Control Circuit Intermittent/Erratic

P2A74 covers brief, recurring faults in the select valve control circuit that clear before a firm low or high verdict. On LNG trucks the valve usually sits near the tank-mounted pump and hydraulic lines, where frame flex, road spray and very cold surfaces around the cryogenic tank stress connectors and insulation. A valve that drops out for a moment can cut hydraulic flow to the working pump mid-stroke; because Westport's control logic recognises the stroke end from pressure changes, such dropouts may also upset pump timing. Typical finds are loose terminals, corroded pins and wiring chafed along the frame rail. No manufacturer publishes P2A74. Wiggle the harness while watching the output status, and check the plug for moisture.

High severity. Can I keep driving?If you smell gas, do not keep driving or start the engine: move away and call for assistance. With no smell, drive moderately to an authorized shop.

Symptoms

Check engine light on, may go out again
Brief hesitation or pressure dips in gas mode
Irregular tank changeover

Most likely causes

Loose terminal in the select valve connector
Moisture or ice in the connector near the cryogenic tank
Harness chafed along the frame rail with intermittent contact

What to check, in order

Start with the simplest. You can tick off each step.

If you smell gas, shut off the supply, ventilate and do not start the engine
Gently move the wiring with the engine running and watch whether the reading changes.
Read the codes with a compatible scanner
Check the connectors and wiring of the component indicated
Leave any work on the gas circuit to an authorized shop

Good to know

Repair difficulty: hard
It can trigger limp mode.
It affects emissions.

What each character of P2A74 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
A: Hybrid or air and fuel
74: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2A74?

If you smell gas, do not keep driving or start the engine: move away and call for assistance. With no smell, drive moderately to an authorized shop.

What causes code P2A74?

The most common causes are: loose terminal in the select valve connector; moisture or ice in the connector near the cryogenic tank; harness chafed along the frame rail with intermittent contact.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.