P0438 code meaning
Catalyst Temperature Sensor Circuit High Bank 2 Sensor 1
Powertrain system Generic code P04xx codes Check engine light
What P0438 means
Some engines – mainly diesels – measure the temperature at or in the catalyst with a thermistor in a voltage divider instead of only modelling it; most makers report exhaust temperature sensors under P0544 ff, P2031 ff or P2080 ff instead. Sensor 1 of bank 2 is the first catalyst temperature sensor on the side without cylinder 1. P0438 means the signal voltage is above its upper limit – typically the sensor or its wiring is open, or the signal is shorted to positive. No manufacturer document available to us uses this code; the description follows CARB, which requires input circuits to be checked for circuit faults and plausibility, and the comparable exhaust temperature sensors.
P0438 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 1.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0438
- Check engine light on
- Usually no noticeable change (substitute value from the model)
- Diesel: filter regeneration distorted or blocked, possibly further codes such as P2459 or P0420
Common causes of P0438
- Most likelySensor or wire open (broken by vibration or heat)
- Most likelyConnector off or loose, ground wire open
- Less likelySignal wire shorted to positive
- Less likelyEngine module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Catalyst temperature sensor b2s1Sensor wiringEngine control module
What each part of P0438 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 38 | The exact fault in that area. |
What to do next
- Note P0438 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0438
What does P0438 mean?
P0438 means "Catalyst Temperature Sensor Circuit High Bank 2 Sensor 1". Some engines – mainly diesels – measure the temperature at or in the catalyst with a thermistor in a voltage divider instead of only modelling it; most makers report exhaust temperature sensors under P0544 ff, P2031 ff or P2080 ff instead. It is a generic code, so it means the same on every make.
Is it safe to drive with P0438?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0438 fail an emissions test?
Yes, it can. P0438 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0438 to fix?
Difficulty: medium. A typical repair takes 0.5 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0438 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.