Some heavy-duty LNG systems do not drive the cryogenic tank pump directly but through hydraulics: an engine- or motor-driven hydraulic pump supplies oil to a reciprocating hydraulic drive on each tank pump. Westport's patent US8726785B2 shows two LNG vessels whose pumps sit inside the tanks, plus a selector valve that the controller switches to decide which pump receives hydraulic flow. P2A70 covers the electrical control circuit of such a select valve and is set when the driver output detects a general fault. If the valve cannot be commanded, the system may be stuck on one tank or lose LNG supply. No manufacturer publishes P2A70; CARB's heavy-duty rule requires output components to be monitored. P2A72 and P2A73 separate the low and high cases.
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
- Fuel drawn from one LNG tank only, range reduced
- Loss of gas supply, dual-fuel engine falls back to diesel-only or derates
Most likely causes
- Damaged harness or connector at the select valve on the frame
- Select valve solenoid coil faulty
- Output stage in the controlling module faulty
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
- It affects emissions.
What each character of P2A70 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- A: Hybrid or air and fuel
- 70: Specific fault in that system
Frequently asked questions
Can I keep driving with code P2A70?
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 P2A70?
The most common causes are: damaged harness or connector at the select valve on the frame; select valve solenoid coil faulty; output stage in the controlling module faulty.
Related codes
- P2A71Alternative Fuel Hydraulic Fuel Pump Select Valve Control Range/Performance
- P2A72Alternative Fuel Hydraulic Fuel Pump Select Valve Control Circuit Low
- P2A73Alternative Fuel Hydraulic Fuel Pump Select Valve Control Circuit High
- P2A74Alternative Fuel Hydraulic Fuel Pump Select Valve Control Circuit Intermittent/Erratic
- P2A75Alternative Fuel Hydraulic Pump Pressure Sensor Circuit
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.