P05EB

Code

Generic P — Powertrain

Cold Start SCR NOx Catalyst Inlet Temperature Too Low

Brand: Generic

Type: P — Powertrain

Views: UK: 24 EN: 66 RU: 34

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Page language: EN

Causes

Faulty SCR inlet temperature sensor (thermistor/RTD)
Open or shorted wiring between sensor and ECM
Poor connector connection (corrosion, loose pin, bent terminal)
Broken or chafed harness or damaged insulation
Sensor installed incorrectly or missing/heavily contaminated
Exhaust leak upstream of the SCR sensor

Symptoms

Check Engine Light (MIL) illuminated
Reduced NOx conversion or disabled SCR dosing strategy
Possible limp mode or derate on some systems
Poor cold-start emissions performance
Stored freeze frame and related NOx or SCR DTCs

What to check

Read and record DTC, freeze frame and related codes with a capable scan tool
Use live data to monitor SCR inlet temperature during cold start and warm-up
Compare SCR inlet temperature to ambient air and exhaust temperatures for plausibility
Visually inspect sensor, connector and wiring for damage, corrosion or disconnection
Check for exhaust leaks upstream of the SCR and at the sensor boss
Measure sensor circuit for correct reference voltage, signal voltage and continuity

Signal parameters

Sensor type: typically thermistor (NTC) or RTD — outputs resistance or a scaled voltage to ECM
Typical signal range: sensor circuit uses the vehicle reference (0–5 V) and will report a voltage corresponding to temperature
Expected behavior: during cold start the inlet temperature value should rise gradually as exhaust heats; a persistently very low reading is abnormal
Use live-data graphs: SCR inlet temp vs time, compare to exhaust manifold/cylinder head temp sensors

Diagnostic algorithm

Verify the code and freeze frame data with a scan tool. Note ambient and reported SCR inlet temperature at startup.
Inspect sensor and harness visually for obvious damage, contamination, or loose connectors. Repair any physical problems.
With connector disconnected, measure sensor resistance and compare to OEM specification (or check resistance change with applied heat/cold). If the sensor is out of spec, replace it.
With ignition on, backprobe the sensor connector and verify reference voltage (if applicable), signal voltage, and ground continuity to the ECM using wiring diagram references.
Check continuity between the sensor and ECM pins; repair any open or shorted circuits. Wiggle test wiring to reproduce intermittent faults.
Inspect for and repair any exhaust leaks upstream of the SCR sensor mounting that could cause erroneous low temperature readings at the sensor location.

Likely causes

Defective inlet temperature sensor
Connector corrosion or loose terminal
Open circuit or short to ground/power in sensor circuit
Exhaust leak or physical damage near sensor mounting
Aftermarket or wrong part sensor with different characteristics

Fault status

⚠️ Status

Cold Start SCR NOx Catalyst Inlet Temperature Too Low — ECM detected the SCR inlet temperature reading below the expected threshold during cold-start conditions. May affect SCR dosing and emissions control; further diagnosis required.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours