1991 Chevrolet K1500.4.3 V6. Temp guage is all the way to hot. I replaced the temp sensor on the side of the block. Didn’t help. It’s possible that the guage is bad. How likely is it that the temp sensor on top of the engine near the thermostat housing is bad?
Coolant temp sensor
- Thread starter otis24
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The temp sensor with the two wires one black and one yellow is for the ECM.
The other temp sensor will most likely have a single wire and that is for the gauge.
If you disconnect the single wire temp sensor, the gauge should read cold.
If you disconnect the two wire temp sensor, the check engine light should come on.
The other temp sensor will most likely have a single wire and that is for the gauge.
If you disconnect the single wire temp sensor, the gauge should read cold.
If you disconnect the two wire temp sensor, the check engine light should come on.
It's fairly likely that your 31 year old sensor has gone bad.
Make certain your engine doesn't use a 12 volt sender for the gauge and a 5 volt sensor for the ECU.
Make certain your engine doesn't use a 12 volt sender for the gauge and a 5 volt sensor for the ECU.
I know that when I unhook the one wire sensor the guage goes cold. So what happens if I unhook the 2 wire sensor. Check engine light means good. No CEL means bad?
If you unhook the 2 wire sensor, you will eventually get a CEL, it might take several minutes (engine must be running). If the 2 wire sensor is bad you should also eventually get a CEL. If you aren't getting a CEL with the sensor connected you can be pretty sure it's OK.
Since unhooking the one wire sensor makes the gauge read cold, that tells you the gauge and it's wiring is probably OK.
You could possibly have a short to ground in the sensor wire somewhere near the sensor, a short to ground will peg the gauge on hot. Might want to disconnect the wire from the sensor and wiggle it while having someone watch the gauge.
The sensor is most likely bad, though. And I'd start by replacing that unless the wiring is obviously damaged.
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The one-wire sensor is only for the gauge. A failure of this sensor will not cause a CEL.
The two-wire sensor is only for the ECM. A failure of this sensor will not cause the gauge to work incorrectly.
The two-wire sensor is only for the ECM. A failure of this sensor will not cause the gauge to work incorrectly.
Sometimes those senders are switches for idiot lights, make sure you got one for a gauge. Being on the side of the block, I am sure you changed the correct part having one wire. I never seen an ECT sensor for the computer on the side of the block. The top mounted sensor has nothing to do with the gauge. I have seen some flakey gauges lately, I wouldn't rule that out too.
Ok, so I replaced the one wire sensor. It still pegs hot. Either the new sensor was no good, there is a short, or the guage is bad. Correct assessment?
The vehicle is 31 years old. So a faulty guage isn’t out of the question. The odometer quit working 6 years ago. I will move the wire around on the sensor going to the block to see what the guage does.
It's east enough to test temperature sensors that are only just give out a different resistance depending on the temperature. Measure the resistance on a cold engine (and note the outside temperature), then warm up the engine and check it again. I would never replace this sensor unless it tested bad.
Testing the gauge and wiring is going to be just as easy if you have a variable resistor.
Testing the gauge and wiring is going to be just as easy if you have a variable resistor.
To add to what zzy has written, temperature sensors are thermistors (https://en.wikipedia.org/wiki/Thermistor). These are resistors that change resistance as their temperature changes. Most automotive temperature sensors are negative co-efficient sensors. That is, as their temperature increase their resistance decreases.
That's exactly what the chart in my Factory Service manual shows. Decreasing resistance with increasing temperatures.
Did you use an aftermarket sensor or a factory one? It's also a very good chance that the gauge is messed up. For instance the temp gauge in my 92 Cavalier will only go up to the first mark even after I've replaced the temp sensor several times and the thermostat is fairly new and a factory part. The temp sensor in this car is a three wire because it also is the sensor for the ECM as well as the gauge.
