What Does P1620 Mean?
The engine coolant temperature sensor signal circuit has an open or short to battery voltage condition. The PCM is receiving an implausible high voltage signal from the ECT sensor circuit.
Common Causes
35%
Damaged wiring harness with short to battery voltage from chafing on hot components
30%
Failed engine coolant temperature sensor with internal short
20%
Corroded or damaged sensor connector allowing moisture intrusion
10%
Open ground circuit in ECT sensor return path
5%
PCM internal voltage reference or input circuit failure
Diagnostic Steps
1
Step 1: Disconnect ECT sensor connector and measure voltage on signal wire with key on - should read near 0V if wiring is shorted to B+
2
Step 2: Inspect sensor wiring harness routing for contact with exhaust manifold, alternator, or other B+ sources
3
Step 3: Test ECT sensor resistance at various temperatures (typically 2-3k ohms at room temp, varies by manufacturer)
4
Step 4: Check voltage reference circuit at sensor connector - should be approximately 5V with sensor disconnected
5
Step 5: Verify ground circuit continuity and check for voltage drop under load conditions
Estimated Repair Cost
$120 - $650
Parts + labor, varies by vehicle and location
The engine coolant temperature sensor signal circuit has an open or short to battery voltage condition. The PCM is receiving an implausible high voltage signal from the ECT sensor circuit.
The most common cause of P1620 (Engine coolant temperature signal open/short to B+) is: Damaged wiring harness with short to battery voltage from chafing on hot components
Typical repair costs for P1620 range from $120 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Engine may run in fail-safe mode with incorrect fuel mixture and timing. May experience poor fuel economy, rough idle, and potential overheating if cooling fans don't activate properly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1620 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Management/Cooling System
Difficulty
Type
Manufacturer
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