P2A84 is set when pump B's compression stroke valve is electrically sound yet the pump does not respond as commanded. A controller that drives several pumps or elements in turn can compare them: in Caterpillar's multi-element patent, flow results from how often the elements are fired and how long each waits, so an element adding less pressure per command than its neighbours stands out. A slow spool, contaminated oil, internal leakage past the spool or worn plunger seals on the cryogenic side can all reduce pump B's output. With two tank pumps as in Westport's patent, the pressure behaviour before and after a switchover can also be compared. No manufacturer publishes P2A84. Check oil condition and compare delivery with pump A.
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 after several drive cycles
- Lower delivery from one tank or element
Most likely causes
- Spool of valve B slow or leaking internally
- Contaminated hydraulic oil
- Worn plunger seals on the cryogenic side of pump B
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- It can trigger limp mode.
- It affects emissions.
What each character of P2A84 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- A: Hybrid or air and fuel
- 84: Specific fault in that system
Frequently asked questions
Can I keep driving with code P2A84?
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 P2A84?
The most common causes are: spool of valve B slow or leaking internally; contaminated hydraulic oil; worn plunger seals on the cryogenic side of pump B.
Related codes
- P2A83Alternative Fuel Pump B Compression Stroke Valve Control Circuit/Open
- P2A85Alternative Fuel Pump B Compression Stroke Valve Control Circuit Low
- P2A86Alternative Fuel Pump B Compression Stroke Valve Control Circuit High
- P2A80Alternative Fuel Pump A Compression Stroke Valve Control Circuit Range/Performance
- P2A88Alternative Fuel Pump C Compression Stroke Valve Control Circuit Range/Performance
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.