Auto Repair Q&A



Cooling System










Auto Repair Products

Coolant Temperature Sensor

Scan Code Reader

One of those things that can set off your engine light on the dashboard and potentially shut down your vehicle is a coolant temperature sensor reading. In many vehicles, if the coolant temperature sensor says that the engine coolant is too hot, it will not allow the engine to be started until temperatures drop. In some, it will actively shut down the engine or restrict RPMs if the engine is running.

The sensor is meant to keep the engine from overheating and warn if the coolant temperature gets out of range. If your computer throws a temp sensor code, you will need to find out what the problem is - a genuine issue with coolant temp or a malfunction in the sensor or its circuit.

First, the easy checks.

In our forums, this issue came up with dlastuka's 1998 Toyota Camry. Big Block 409 answered with a handful of suggested checks:

Are the cooling fans coming on?
Is the anti-freeze level full?
Is the anti-freeze due to be replaced or (long overdue) to be replaced.

These are important questions and are things that can be answered quickly, without any wrench work or research into the vehicle itself required. If the coolant (anti-freeze) does need replacement and is overdue, then it should be done with a full flush. Most competent DIY mechanics can do this at home. Always be sure to recycle the used antifreeze and tainted water, of course.

Now for deeper diagnosis.

If those did not remedy the problem, then things will need to get a little more in-depth. Mechanic Bfree in our forum addresses this. To do it, you'll need a long-stem thermometer (preferably digital) that you can push down into the radiator to get a relatively accurate temperature reading of the actual coolant in the engine. You'll also need a good computer scan tool - not just a code reader - so you can pull the temp sensor's reading.

Doing this, compare the two numbers and if they are relatively close (within a couple of degrees), then chances are your sensor is OK and the problem is in either the circuit from it to the computer or the coolant distribution or coolant levels. Before you assume this, however, do one more check.

Run a fused jumper wire (important so the circuit can't overload) around the sensor by unplugging it and fusing the two terminals on its plug together. Your scan tool should now be giving an engine temperature reading of over 250 degrees Fahrenheit. If not, then your problem is in the circuit itself - likely a grounding issue or lack of voltage.

Keep Going

Once those checks have been made, you can continue on with your diagnosis now that you've narrowed down the problem.