What causes fault code P042C?

• Most likely: Short circuit to ground in the sensor wiring harness • Likely: Faulty catalyst temperature sensor (internal short) • Possible: Damaged connector or corrosion in the sensor terminals • Rare: Internal Engine Control Module (ECM) failure

Powertrain (Engine & Gearbox)Standard EOBD

P042C - Catalyst Temperature Sensor Circuit Low Bank 1 Sensor 1

Q: What are the symptoms of fault code P042C?

• Check engine light (MIL) illumination • Vehicle may enter 'Limp Home Mode' • Reduced engine performance • Increased fuel consumption • Failed emissions test

Q: How do you fix fault code P042C?

STEP 1: Visually inspect the sensor connector (Bank 1, Sensor 1) for signs of heat damage or corrosion. Clean as necessary. STEP 2: Measure circuit voltage with ignition ON, sensor disconnected. You should see a 5.0V reference. If 0V is present, check for a short to ground in the signal wire. STEP 3: Test sensor resistance. If the sensor shows near 0 Ohms, it is internally shorted. Compare readings with OEM specs (typically 100 Ohms to several kOhms depending on temp). STEP 4: Use a scan tool to monitor live data. If the temperature reads a fixed maximum (e.g., 900°C+) on a cold engine, a short is confirmed. STEP 5: If wiring and reference voltages are correct, replace the catalyst temperature sensor.

Last updated:1 February 2026

Related:Catalyst Temperature Sensor (EGT), Engine Control Module (ECM/PCM), Wiring Harness, Catalytic Converter

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

P042C is set when the Engine Control Module (ECM) detects a low voltage signal from the Catalyst Temperature Sensor 1 on Bank 1. In a typical NTC (Negative Temperature Coefficient) sensor circuit, low voltage is interpreted as an excessively high temperature or a short circuit to ground. The ECM uses this data to monitor the efficiency of the catalytic converter and prevent thermal damage. If the signal voltage drops below a calibrated limit (typically <0.2V) for a predefined duration, the DTC is stored.

Possible Causes

Short circuit to ground in the sensor wiring harness

Faulty catalyst temperature sensor (internal short)

Damaged connector or corrosion in the sensor terminals

Internal Engine Control Module (ECM) failure

Symptoms

Check engine light (MIL) illumination

Vehicle may enter 'Limp Home Mode'

Reduced engine performance

Increased fuel consumption

Failed emissions test

Do you also have
other fault codes?

See how P042C connects with your other fault codes. Our advanced analysis tool identifies causal relationships and root causes directly.

Analyze multiple codes

P042C - Catalyst Temperature Sensor Circuit Low Bank 1 Sensor 1

Related Fault Codes

Technical Description

Possible Causes

Symptoms

Recommended Solution

Workflow

Mechanic's Tip

Do you also have
other fault codes?

P042C - Catalyst Temperature Sensor Circuit Low Bank 1 Sensor 1

Related Fault Codes

Technical Description

Possible Causes

Symptoms

Recommended Solution

Workflow

Mechanic's Tip

Do you also have other fault codes?

Do you also have
other fault codes?