racenjasn

Recently had a blown alternator. About the same time, my temperature gauge started reading incorrect. It just gets off C, but doesn't read the correct temp. I replaced the temp sensor and still not working correct. I say correct, because I can turn off the car while driving at temperature, and turn the car back on to see the gauge reading the standard operating temp.

Any thoughts on what else could be causing this?

FYI - Used a reman alternator and the battery light is still on. Everything checks out fine, but will be exchanging the reman for a new built alternator to get the light to turn off. Had this same issue once before.

ezone

Make absolutely sure the bolts for the alternator are tight, and the brackets are clean. Same for ground cables on the block/trans/chassis/battery.

Poor grounding of the alternator housing can lead to PCM damage, and that's expensive.

Tach, speedo, temp gauges and many warning lights operate using data from the PCM....so a corruption in PCM data may be seen as wacky gauge operation.
If the alt was left loose and the PCM gets damaged because of it, that's trouble. (most people report being stuck in limp home mode after PCM damage though, also zero communication with a code reader or scanner after damage)


You could use a better scanner or app to view live data from the PCM, read what it believes the ECT is and compare to the gauge on the dash. PCM reading anywhere form 170*F to about 220*F will have the needle right about in the center of the gauge.

OTOH it could be a simple gauge stepper motor going flaky. Do a gauge module self test to make all the needles sweep, see if they all work correctly.

racenjasn

Tried the self check and everything was good with all 8s. Hopefully the new alternator will do the trick. I filed all the contacts for the top mount and hot wire, but didn't do the ones on the bottom bracket. I will this time.

I will report back in a couple of days. Thanks.

racenjasn

Installed a brand new alternator (not a reman) and still the same issue. Every surface was sanded/filed to make sure of a good connection.

Any other ideas?

If I shut the car off once it has reached normal operating temp (guessing as the gauge doesn't initially work) and then turn the car back on, the gauge works. Doing that has solved the torque converter not locking up and the CE light coming on because of the O2 sensors (too rich).

ezone

Is the battery light still staying on?

Key on, engine off: Unplug the 4 wire round connector from the alternator, see if the battery light goes out.
If it goes out, the issue is inside the alternator.
If it stays on, more checks are needed.

Follow a troubleshooting guide for the warning light staying on in a service manual. I think part of that is checking the gauges self test, do all of the warning lights blink on and off during the test? Did the battery light blink along with the rest, or did it do something else?

I didn't follow here. Are you saying there are fault codes that disappear after cycling the key?


Do you have a scanner that can display live engine operating data from the PCM? You need to see what the PCM is seeing. Figure out what the PCM thinks the coolant temperature is when the gauge isn't showing correctly.

Also try to look in the rest of the data to see if anything else makes a drastic change when the key is cycled.

cd4th

I'll follow this thread for a bit and see what you come up with. I have a 2003 LX that has done the same deal with the temp gauge since I've owned it. (https://www.civicforums.com/forums/1...ml#post4666213) I've connected my scanner while running the car and the scanner shows the temp operating correctly but 99.9% the gauge seldom moves until I restart. A self-test of the dash shows no problems, and I've never looked for another dash to swap and try.

racenjasn

Sorry to say, but I won't be able to help any longer. The rubber timing cover gasket got loose between the gear and the belt and it skipped time. After warmup, I get multiple cylinders misfire.

Before that, I drilled out the alternator mount and used a straight through bolt to make sure everything was tight. All contact points were filed clean. The negative battery cable was removed, cleaned and contact points on the body and engine cleaned and reinstalled. A new grounding strap was installed. The battery light stayed on.

I used my scanner to see the live data and the ECM was seeing correct and rising temps but it wasn't registering on the temp gauge. The test/sweep worked fine. Guessing it was a computer issue.

Carbuff2

Do the gauge and ECU use the same senders?

ezone

On a 7th gen Civic (01-05) and newer, sort of.
The ECT sender is not connected directly to the gauges, but:

The PCM reads the coolant temp sender.

The gauge cluster microprocessor uses data from the PCM to operate the coolant temp, tach and speedo gauges, and some warning lights.

HTH