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Discussion Starter · #1 ·
After picking up my truck the mechanic mentioned that my dash temperature gauge was bouncing all over the place, setting off the “check gauges” warning light.

Since there is a delta between the coolant and oil temp I watched my oil temp on my Scangauge 2 on the drive home.

Dash gauge would jump around, drop to bottom of gauge, then peg out, and then would go dead center on the gauge between C / H , like normal, stay there for a while and repeat the cycle. The whole time the gauge was acting squirrelly my oil temperature stayed right at 200 degrees and when I slowed down or came to a stop oil temp would go down a few degrees.

Any thoughts on what I should be checking, or just a faulty sensor? I have been having an extremely small drip of coolant on the garage floor before I took it to Steinacher Automotive. I don’t know if it’s the water pump vent or thermostat housing but I plan on flushing and replacing both. Degas bottle is still just barely below the Full mark.

Thanks........ Big Horn
 

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I'd pull the wire off of the sensor and see what it does

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Bugman's troubleshooting is a good first step. Sounds like it might be a loose connection or a wire that's intermittently open. Or the sensor is bad. But check the wiring first.
 

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Discussion Starter · #4 ·
I'd pull the wire off of the sensor and see what it does

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Bugman's troubleshooting is a good first step. Sounds like it might be a loose connection or a wire that's intermittently open. Or the sensor is bad. But check the wiring first.
Thank you Gentlemen, I got the tuner put back on today and checked the plug on the coolant sensor. It was snapped in place correctly. I removed it and pins and plug look good, no corrosion. The wiring that is exposed past the loom looks good also.

Where would I go to check continuity, from plug to dash gauge? Also, I did a search in the Diesel Stop archives, it looks like manual trucks have an additional sensor, but A/T only have the one - is this correct?

When I started the truck cold this morning the gauge went straight to HOT and the check gauges light illuminated and then began to flutter. As the coolant sensor does not feedback to the computer on our trucks am I to assume it’s just the one sensor, the wiring, and the dash gauge, and from what I’ve read if the gauge in the dash is bad the whole dash (gauge assembly) has to be sent off for repair?

Thanks again!!
 

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There are 2 sensors for
for the coolant. One for the gauge on top of the waterpump and the one for the light on the front passenger side of the block I believe.

I can't help much on where and what wires to check on the firewall pass through connector or under the dash.

If you do decide to send it off I used RT Grim & Company. They have next day shipping with UPS both to them and back. Overall it is still about a week.


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Discussion Starter · #6 ·
There are 2 sensors for
for the coolant. One for the gauge on top of the waterpump and the one for the light on the front passenger side of the block I believe.

I can't help much on where and what wires to check on the firewall pass through connector or under the dash.

If you do decide to send it off I used RT Grim & Company. They have next day shipping with UPS both to them and back. Overall it is still about a week.


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Thanks bugman! And I guess I didn’t read your previous post correctly🙄 when I get a chance I’ll unplug the sensor by the water pump and see what the gage does👍
 

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No problem, sometimes I have to go back and redo what I thought that I had done.

Here is the link to RT Grimm & Co. Instrument Cluster Repair & Car Electronics Repair & Sales | R T Grim Co

From what you are describing it is sounding more like a wire or gauge problem leaning more to the gauge. I believe that if it was a wire problem the problem would be steady and not jumping all over the place. But with these new type of gauge clusters you never know, it could even be a broken circuit board on the cluster.
 

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If the wiring had insulation rubbed thru, it might cause that intermittent problem. Not sure which way the sensor works, but if the two wires rubbed together it might show hot.
As far as I know, my truck only has one coolant temp sensor, running to the instrument panel only and not the PCM. I know of none down on the passenger side of the engine. Just checked the wiring diagrams and there's only one coolant temp sensor on an 02. Ford calls it "Coolant Temperature Sensor 2" for some reason, but it's the one located on the water pump.
But a gauge issue might be high on the list as well.

If you want to dig into the wiring more, I can dig up the connector pinouts for you.
 

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Discussion Starter · #9 ·
If you want to dig into the wiring more, I can dig up the connector pinouts for you.
That would be great Kevin, i would appreciate that. If I’m able to eliminate the wiring and the sensor as the problem then I know I’ll need to send the gage cluster off for repair.

As an update, we drove the truck 60 miles tonight, ran fantastic, but now the gage stays pegged all the way to HOT and then will swing and peg out all the way to the COLD with no fluttering and the “check gage” light staying on constant.
 

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Discussion Starter · #10 ·
I'd pull the wire off of the sensor and see what it does

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Got that done today, with the plug disconnected from the sensor the gage needle rests at the bottom of the gage, and no “check gauges” light, will be less of a distraction while driving.

I read a similar post from 2008. As the sensors’ resistance changes as it heats up the OP jumped across the plug with a 480R resistor, which made the temperature gage read normal.

I jumped across it with a 322R and a 470R resistor, and in both cases the gage pegged all the way to HOT and the “check gauges” light stayed on. So, I think this does point to a short in the wiring or a bad gage cluster as bugman and klhansen noted.

Taped off sensor and plug until I can check the wiring.
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I think that I'd try a new sensor.

They should only be around $20

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Yep, if the gauge reads cold with the sensor disconnected, I would definitely try a new sensor. Could be shorted internally.
 

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Discussion Starter · #13 ·
FIXED!! Thank you bugman and Kevin

Went to NAPA, figured as long as I was draining down the coolant level I would install the top radiator hose that goes around the serpentine belt (9066).

After installing sensor and refilling coolant I started the truck, gage immediately went half way and began climbing as the truck warmed up, went to HOT, and set off check gage light again! 😬🥵

But the gage was working sort of, hey wait a darn minute🧐, I called NAPA and said check this temp sender # you sold me, I don’t think the resistance is correct for my truck...... Salesman came back “oh buddy - sorry, we sold you the wrong one, that’s for a gas engine”

So another round trip, and installed NAPA temp sender
TS4047, refilled coolant again, started truck and the gauge needle was towards the bottom and started rising slowly......stayed right in the middle at full operating temperature😗

Speedometer Vehicle Car Gauge Steering wheel


Woohooo!
 

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Sometimes it is the simple things that give us the most problems. Glad it's fixed.

On the simple things, a few years ago I had a ABS light. I read the code and it came up the VSS, so I replaced it and the ABS light went away. But then when I got up to 45 mph and above my speedometer would start to do the funky chicken and bounce all over the place along with cutting the cruse off, so I changed out the VSS again.....same thing.

I then tested out the wiring from the VSS to the cluster....all OK.

So I pulled the cluster and sent it off, I got it back and had the same problem.

Then one day I was under my truck near the rear end and noticed that the VSS looked like it wasn't seated all the way into the housing. I had just pushed it in with my hand so I grabbed a rubber mallet and tapped it down the rest of the way.

I took a drive and all was well

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I love it when a plan comes together. :D
And now you'll have the complete wiring and instrument panel troubleshooting for the next time.
 
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