What it means
The pressure signal of alternative fuel tank B does not match plausibility checks against tank temperature and fill level. Sensor drift.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The tank B pressure sensor reports alternative-fuel tank pressure to the AFCM. The module checks whether that reading is plausible alongside tank temperature and fill level, and sets P2A42 when the relationship does not make sense. Sensor drift or loose mounting can bias the reading even when the circuit is not simply open or shorted.
Common causes
Most likely first.
- Sensor zero drifted
- Sensor mounting loose - bias offset
- Sensor element aged beyond calibration window
Symptoms
- Check-engine light
- Alternative-fuel warning light
- Inaccurate tank pressure or fuel-level indication
How to diagnose it
- Save freeze-frame data and compare tank B pressure, temperature, and fill-related live data to see which values appear inconsistent.
- Check whether the reported tank pressure changes plausibly with known fill and temperature conditions, allowing for the vehicle’s design and service information.
- Inspect the tank B pressure sensor for loose mounting, damage, or contamination that could bias its measurement.
- Check the sensor connector and wiring for poor contact, and verify power, ground, and signal against the manufacturer’s specification.
- If the circuit and mounting are sound, test the tank B sensor for drift using the specified diagnostic procedure.
Common fixes
- Secure the tank B pressure sensor if its mounting is loose.
- Repair poor connector contact or damaged wiring to the sensor.
- Replace the tank B pressure sensor if it is out of calibration per the specified test.
Can I keep driving?
The system may misreport tank pressure or fuel level and limit alternative-fuel operation. If gasoline operation is normal, keep driving limited until the reading is verified, and do not rely on the displayed tank information.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.