P2A85: Alternative Fuel Pump B Compression Stroke Valve Control Circuit Low

P2A85 means the drive output for pump B's compression stroke valve reads too low for its commanded state. Typical are a control wire chafed through to the frame, which can keep the solenoid energised even when the controller wants it off, or a coil with shorted windings that draws excessive current. A valve stuck in the fill position leaves pump B's plunger parked at full extension; the pump stops delivering, and pressurised oil remains on its drive side. Caterpillar's six-element example can partly make up for this with the remaining elements, whereas a two-tank system loses the second tank's supply. No manufacturer publishes P2A85. Compare the measured coil resistance with that of an identical A or C valve.

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

Warning lamp on
Pump B delivers nothing, reduced power or range

Most likely causes

Control wire of valve B chafed through to the frame
Coil of valve B with shorted windings
Output stage for valve B shorted

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
With the connector unplugged, check whether the signal wire is making contact with ground.
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 P2A85 means

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

Frequently asked questions

Can I keep driving with code P2A85?

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 P2A85?

The most common causes are: control wire of valve B chafed through to the frame; coil of valve B with shorted windings; output stage for valve B shorted.

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.