Engine Coolant Temperature Sensor 1
Indicates a fault with the engine coolant temperature sensor 1.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The engine coolant temperature sensor measures how hot the coolant is, which helps the computer adjust fuel and timing. If it's reading incorrectly, the engine may run poorly or not start at all.
What the computer is actually seeing
The engine control module (ECM) expects a voltage signal proportional to the coolant temperature. This should range from 0.5V (cold) to 4.5V (hot).
What a healthy reading looks like
At normal operating temperature (195-220°F), expect around 2.5V to 3.5V from the sensor.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 1Check coolant level and ensure it's between the min and max marks. Decision point: Is the coolant level okay?
- 2Inspect wiring and connector for damage or corrosion. Decision point: Are there any visible issues?
- 3Monitor the voltage from the engine coolant temperature sensor while the engine is running. Decision point: Is the voltage reading within expected range?
- 4If voltage is out of range, replace the engine coolant temperature sensor. Decision point: Did replacing the sensor fix the issue?
Common causes
- Faulty engine coolant temperature sensor
- Wiring issues (shorts, opens, corrosion)
- Connector problems (loose pins, dirty contacts)
- Incorrect coolant level or air in the system
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's safe to drive short distances, but you may experience poor engine performance.
What happens if this fault returns?
If the fault returns after you clear it, it could indicate a persistent issue with the sensor or wiring.
Why does this code pair with SPN 0594?
SPN 0594 relates to the same circuit for the second temperature sensor, it's common to see both if there's a system-wide issue.
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