P0426: Catalyst Temperature Sensor Circuit Range/Performance Bank 1 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. Sensor 1 of bank 1 is the first catalyst temperature sensor on the side with cylinder 1. P0426 means the signal is electrically valid but implausible – compared with the temperature model or neighbouring exhaust sensors it is off, sluggish or frozen. Only FCA's 3.0-litre EcoDiesel (Ram 1500 and Jeep Grand Cherokee, 2014/15) is documented with this sensor: it sits in the middle of the oxidation catalyst and particulate filter unit, a platinum element with 200–240 Ω at room temperature; the bulletin for P0426 advises blowing soot off the tip, measuring and replacing it, plus a software update.

Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.

Symptoms

• 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

Most likely causes

• Soot on the sensor tip (diesel)
• Sensor aged, characteristic drifted
• Contact resistance in connector or wiring
• Engine module software (plausibility limits)
• Exhaust leak upstream of the sensor

What to check, in order

Start with the simplest. You can tick off each step.

1. First resolve any misfire or fuel mixture codes
2. Compare the reading with other engine data while varying the engine speed.
3. Look for exhaust leaks between the engine and the second sensor
4. Use live data to compare the signals from both oxygen sensors
5. Check for a blockage by measuring exhaust back pressure
6. Replace the catalytic converter only at the end of the diagnosis

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P0426 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 4: Emissions
• 26: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0426?

You can usually keep driving, unless you notice a loss of power, which may point to a blockage. The car may not pass an emissions inspection.

What causes code P0426?

The most common causes are: soot on the sensor tip (diesel); sensor aged, characteristic drifted; contact resistance in connector or wiring.

Related codes

• P0425Catalyst Temperature Sensor Circuit Bank 1 Sensor 1
• P0427Catalyst Temperature Sensor Circuit Low Bank 1 Sensor 1
• P0436Catalyst Temperature Sensor Circuit Range/Performance Bank 2 Sensor 1
• P042BCatalyst Temperature Sensor Circuit Range/Performance Bank 1 Sensor 2
• P0544Exhaust Gas Temperature Sensor Circuit Bank 1 Sensor 1
• P0420Catalyst System Efficiency Below Threshold Bank 1

Sources

• law.cornell.edu: 13 CCR 1968.2
• static.nhtsa.gov: MC 10151745 9999
• static.nhtsa.gov: MC 10139782 9999
• hella.com: checking the exhaust gas temperature sensor

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.