P2A73: Alternative Fuel Hydraulic Fuel Pump Select Valve Control Circuit High

P2A73 signals that the select valve control circuit sits at a higher voltage than the commanded state allows. Typical faults are an open coil or broken wire on a low-side driven valve, which leaves the line at supply voltage, or a short to battery voltage that the output cannot pull down. The valve then stays in its spring-return position, so hydraulic flow keeps going to one tank pump whatever the command. On a multi-tank LNG truck the second tank may never be used, and the engine runs short of gas although LNG remains on board. Caterpillar's patent shows such a valve shifted by an actuator under controller command. No manufacturer publishes P2A73. Check coil resistance, the connector and the supply wire.

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
Second LNG tank not used, range clearly shorter
Gas supply stops although fuel remains

Most likely causes

Valve coil or control wire open
Control wire shorted to battery voltage
Corroded connector pins with very high resistance

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
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
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 P2A73 means

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

Frequently asked questions

Can I keep driving with code P2A73?

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 P2A73?

The most common causes are: valve coil or control wire open; control wire shorted to battery voltage; corroded connector pins with very high resistance.

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.