Powertrain (Engine & Gearbox)Standard EOBD

P042B - Catalyst Temperature Sensor Circuit Range/Performance (Bank 1 Sensor 2)

Q: What are the symptoms of fault code P042B?

• Check Engine Light (MIL) illumination • Engine may enter Limp Home Mode (reduced power) • DPF regeneration may be inhibited (on diesel engines) • Increased fuel consumption • Failed emissions test

Q: What causes fault code P042B?

• Most likely: Faulty Catalyst Temperature Sensor (Thermal fatigue) • Likely: Corrosion or poor connection in the sensor connector • Possible: Damaged wiring harness (chafed against chassis or exhaust shield) • Rare: Exhaust leak upstream of the sensor affecting the temperature reading • Rare: ECU software issue requiring an update

Q: How do you fix fault code P042B?

STEP 1: Inspect the sensor connector for signs of melting or corrosion. Clean with contact cleaner if necessary. STEP 2: Perform a resistance check on the sensor (unplugged). At 20°C (68°F), it should typically measure 200-500 Ohms (refer to OEM specs). Replace if O.L or shorted. STEP 3: Use a scan tool to monitor Live Data. Compare Sensor 1 and Sensor 2 during warm-up; they should track each other logically. STEP 4: Check the exhaust system for leaks near the sensor that could cause false low readings. STEP 5: Replace the sensor and clear the fault codes. Perform a forced DPF regeneration if required (diesel models).

Last updated:1 February 2026

Related:Katalysatortemperaturgivare, Exhaust Temperature Sensor, Engine Control Unit (ECU), Wiring Harness, Diesel Particulate Filter (DPF)

System

Powertrain (Engine & Gearbox)

Related Fault Codes

P0400

Exhaust Gas Recirculation Flow Malfunction

P0401

Exhaust Gas Recirculation (EGR) Flow Insufficient Detected

P0402

Exhaust Gas Recirculation Flow Excessive Detected

P0403

Exhaust Gas Recirculation (EGR) Control Circuit

Technical Description

P042B is triggered when the Engine Control Unit (ECU) detects an implausible signal from the Catalyst Temperature Sensor 2 on Bank 1. This sensor is typically a thermistor that monitors exhaust gas temperature (EGT) downstream of the primary catalyst. The ECU uses this data to protect exhaust components and verify catalyst efficiency. The code 'Range/Performance' implies that the sensor circuit is electrically intact, but the data provided is illogical compared to other sensors (like Sensor 1 or Intake Air Temp) during specific engine loads.

Possible Causes

Faulty Catalyst Temperature Sensor (Thermal fatigue)

Corrosion or poor connection in the sensor connector

Damaged wiring harness (chafed against chassis or exhaust shield)

Exhaust leak upstream of the sensor affecting the temperature reading

ECU software issue requiring an update

Symptoms

Check Engine Light (MIL) illumination

Engine may enter Limp Home Mode (reduced power)

DPF regeneration may be inhibited (on diesel engines)

Increased fuel consumption

Failed emissions test

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P042B - Catalyst Temperature Sensor Circuit Range/Performance (Bank 1 Sensor 2)

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P042B - Catalyst Temperature Sensor Circuit Range/Performance (Bank 1 Sensor 2)

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Symptoms

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Mechanic's Tip

Do you also have other fault codes?

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other fault codes?