DTC P0011A – Engine Coolant Temperature (ECT) Sensor 1/2 Correlation.

✅ DTC P0011A – ECT Sensor 1/2 Correlation

This code means:

Your vehicle has two coolant temperature sensors (ECT1 & ECT2).
The ECU compares both sensors.
If their temperature readings are too far apart, the ECU triggers P0011A.

🔧 Common Causes

1. Faulty ECT Sensor 1 or ECT Sensor 2

2. Poor wiring connection to either sensor

3. High resistance in wiring harness

4. Ground issue for ECT sensors

5. Coolant not circulating properly (air lock, low coolant)

6. Thermostat stuck open/closed

7. Engine overheating or running too cold

🛠️ Step-By-Step Diagnosis

1. Scan Tool Data Comparison

Read ECT1 and ECT2 live data.

When engine is cold (morning start), both should read ambient temperature (within 3–5°C difference).

When engine warms up, both should increase smoothly and similarly.

❗ If difference >10°C → Correlation fault likely.

2. Check Coolant Level & Flow

Low coolant = wrong sensor readings

Check for air pockets

Bleed cooling system if needed

3. Wiring and Connector Inspection

Check ECT1 and ECT2 connectors:

Terminals loose?

Corrosion?

Broken wires?

Oil or coolant contamination?

Perform:

• Wiggle test
• Back-probe voltage test

4. Sensor Resistance Test (Ohm Test)

Disconnect sensor and check resistance:

Typical ECT sensor (NTC type):

20°C → ~2.5k – 3k ohms

80°C → ~300 – 350 ohms

If one sensor is out of range → replace it.

5. Thermostat Check

If thermostat is stuck:

Stuck open → engine slow to warm → sensors mismatch

Stuck closed → overheating → sensors mismatch

Replace thermostat if temp behavior is abnormal.

6. Check ECU Ground / Reference Voltage

Both sensors share:

5V reference

Ground

Check using multimeter:

Ref voltage: 4.9–5.1V

Ground drop: 0–0.1V

Bad ground = different readings → correlation fault.

🔧 Repairs That Usually Fix P0011A

🎀 Replace faulty ECT1 or ECT2 sensor
🎀 Repair damaged wiring
🎀 Fix poor connectors
🎀 Refill and bleed coolant
🎀 Replace stuck thermostat
🎀 Clean ECU ground points.

🧪 After Repair

Clear codes

Warm engine to operating temperature

Recheck ECT1 vs ECT2 live values

Confirm readings match (within 3–5°C)

Welcome To Madurai Car Service 💐🙏.