What it means
Same as P242A with the signal in plausible range yet not matching the engine model.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The Bank 1 Sensor 3 exhaust gas temperature sensor measures exhaust temperature at its location in the Bank 1 exhaust. The control module sets P242B when the signal stays within an electrically plausible range but does not change as expected for engine and exhaust conditions, suggesting a drifting sensor or circuit problem.
Common causes
Most likely first.
- Exhaust gas temperature sensor drift or failure
- Damaged or high-resistance wiring
- Poor sensor connector contact
Symptoms
- Check-engine light on
- Reduced power or limited regeneration, if enabled by the vehicle
How to diagnose it
- Record freeze-frame data and compare Bank 1 Sensor 3 live temperature with other exhaust-temperature readings and the operating conditions that set the code.
- With the exhaust cool, inspect the Sensor 3 connector and harness for heat damage, chafing, corrosion, or loose terminal fit.
- Watch the Sensor 3 reading from a cold start through warm-up to see whether it changes plausibly rather than lagging or disagreeing with related sensors.
- Check sensor and wiring performance using the manufacturer’s procedure and specifications, including connector contact quality.
- After repair, clear the code and confirm the Sensor 3 reading tracks exhaust warm-up without the fault returning.
Common fixes
- Secure or repair a poor Bank 1 Sensor 3 connector contact.
- Repair damaged or high-resistance sensor wiring.
- Replace a confirmed drifting or faulty Bank 1 Sensor 3 sensor.
- Repair a verified module-side circuit fault.
Can I keep driving?
Drive gently and avoid towing or sustained high loads while the temperature reading is unreliable. The module may limit regeneration or exhaust protection, which can lead to reduced power or after-treatment issues.
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.