P042D

Code

Generic P — Powertrain

Catalyst Temperature Sensor Circuit High Bank 1 Sensor 2

Brand: Generic

Type: P — Powertrain

Views: UK: 24 EN: 59 RU: 41

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Page language: EN

Causes

Failed/shorted catalyst temperature sensor (Bank 1, Sensor 2)
Wiring short to battery voltage or open/short in sensor circuit
Poor or corroded connector or pin contact at the sensor
Damaged wiring harness near exhaust (heat damage, chafing)
Faulty sensor heater circuit (if equipped) or blown fuse
Exhaust leak or plugged/overheated catalytic converter affecting readings

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
Failed or incomplete catalyst monitor readiness
Possible failed emissions test
Usually no driveability symptoms (engine runs normally) but potential for decreased fuel economy or increased emissions

What to check

Retrieve freeze frame and live data with a scan tool; confirm P042D and note conditions when set (engine temp, load, RPM)
Visually inspect sensor, connector, and wiring along the exhaust for heat damage, chafing, or corrosion
Backprobe sensor connector and observe live temperature/voltage signal while engine is cold then warming up
Check for continuity to power and ground; check for shorts to battery voltage
Measure sensor resistance (thermistor) or millivolt output (thermocouple) and compare to specification if available
Inspect heater fuse/relay and measure heater circuit current if sensor has a heater

Signal parameters

Generic downstream catalyst temp sensors produce a temperature-proportional signal; exact units vary by manufacturer
Typical electrical ranges: 0–5 V signal for voltage-output sensors (varies by OEM). Thermistor resistance decreases as temperature rises; thermocouple outputs in millivolts.
Heater circuit (if equipped) normally draws small current; typical heater current is
Downstream sensor (Bank 1 Sensor 2) normally reads lower than upstream sensor once catalyst is at operating temperature; a consistently abnormally high reading on Sensor 2 triggers this code.
Consult OEM service data for exact voltage/resistance/temperature specifications before replacement

Diagnostic algorithm

Verify the code: Read all stored codes and freeze frame data. Confirm P042D is current and note operating conditions when it set.
Visual inspection: Examine sensor, connector, and wiring for damage, melting, corrosion or disconnection. Repair obvious damage before further testing.
Scan-tool observation: Monitor Bank 1 Sensor 1 and Sensor 2 temperature/voltage/reading values while cold and during warm-up. Compare downstream sensor to upstream; look for sudden spikes or constant high values.
Connector/power checks: With ignition ON, check for battery voltage where expected, and verify good ground for the sensor circuit. Check fuses/relays for heater circuit if present.
Backprobe and measure: With engine running and cold-to-hot transitions, backprobe the sensor signal wire. Measure voltage or millivolt output and compare to expected behavior (signal should vary with temperature).
Resistance measurement: If thermistor type, remove sensor and measure resistance vs temperature (compare to OEM spec or confirm it changes smoothly when heated/cooled).
Wiggle and continuity test: Wiggle wiring harness while watching live data or DVM for intermittent faults. Check continuity and for shorts to battery or ground.
Isolate sensor: If safe/possible, swap with identical downstream sensor on other bank (if same type) or temporarily substitute a known-good sensor to see if code follows the sensor.
Inspect catalytic converter and exhaust: Look for restrictions, melting, or external damage; an overheated converter can cause true high temperatures at the downstream sensor.
Repair or replace: Repair wiring/connector faults or replace the sensor if it fails electrical/functional tests. Replace catalytic converter only if diagnosis confirms converter fault and OEM procedures indicate replacement.
Clear codes and test-drive: Erase codes, ensure monitors complete, and verify the code does not return under the reported conditions.

Likely causes

Sensor wiring shorted to 12V (causing high voltage reading)
Thermistor/thermocouple sensor internally failed and reporting high temperature
Connector corrosion or poor ground causing erroneous high reading
Physical damage from excessive exhaust heat or debris

Fault status

⚠️ Status

PCM detected a high condition on the Bank 1 Sensor 2 catalyst temperature sensor circuit (voltage/temperature above expected threshold). This may set the MIL and affect catalyst monitoring.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.8-2.5 hours