P2A42: Alternative Fuel Tank B Pressure Sensor Range/Performance
The pressure signal of alternative fuel tank B does not match plausibility checks against tank temperature and fill level. Sensor drift.
What P2A42 means
P2A42 is a generic OBD-II powertrain code in the fuel & air group. In plain English: the signal is within electrical limits but doesn’t make sense compared with other readings, so the part or system isn’t performing as expected.
- Check engine light
- Usually on
- Emissions-related
- Yes — can fail inspection
- Limp mode possible
- Yes
- Drive cycle to clear
- Not required
Get it fixed
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Common causes
- 01Sensor zero driftedMost likely
- 02Sensor mounting loose - bias offsetPossible
- 03Sensor element aged beyond calibration windowLess likely
Can I drive with P2A42?
Not recommended beyond getting it to a shop.
This fault can put the engine or transmission in limp mode with reduced power, which can make merging and passing unsafe. Have it diagnosed as soon as possible.
Why we rate it urgent
- Can put the vehicle in limp mode (reduced power)
- Turns on the check engine light
- Emissions-related: will usually fail an OBD inspection
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose P2A42
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just P2A42. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Check for related codes first
Look for P2A47. Related codes often share a cause; a circuit or sensor code usually needs fixing before a performance code like this one.
- 3
Check live data
Watch the related sensor and actuator readings in live data (Alt fuel tank B pressure sensor, Wiring harness, AFCM) and compare them with expected values in the service information for your vehicle.
- 4
Test the likely causes in order
Start with the most likely cause and work down: Sensor zero drifted; sensor mounting loose - bias offset; sensor element aged beyond calibration window. Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and drive the car under the conditions in the freeze-frame data to confirm it does not return.
P2A42 repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Moderate
- Good DIY job?
- Usually a shop job
Needs a scan tool and some experience with testing.
Parts and systems involved
- Alt fuel tank B pressure sensor
- Wiring harness
- AFCM
P2A42 FAQ
What does P2A42 mean?
P2A42 means “Alternative Fuel Tank B Pressure Sensor Range/Performance”. The pressure signal of alternative fuel tank B does not match plausibility checks against tank temperature and fill level. Sensor drift.
Is P2A42 serious? Can I keep driving?
We rate P2A42 as urgent severity. Not recommended beyond getting it to a shop. This fault can put the engine or transmission in limp mode with reduced power, which can make merging and passing unsafe. Have it diagnosed as soon as possible.
What causes P2A42?
The most common causes, from most to least likely: Sensor zero drifted; Sensor mounting loose - bias offset; Sensor element aged beyond calibration window. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix P2A42?
Typical labor is about $125–$500 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix P2A42 myself?
DIY difficulty is moderate. Most owners leave this to a shop because it needs involved testing or specialist tools. Always confirm the cause before buying parts.
Will P2A42 clear itself?
If the fault was intermittent, the warning may go off once the computer stops seeing it, but the code stays in memory. Fix the cause; clearing the code alone doesn’t repair anything.