1990 K5 5.7L OBD1 code 15

[Slade001]

(15 coolant sensor circuit low or open)

Been getting the SES light after drives over 10 minutes or so.
Just replaced the radiator, both hoses, the thermostat and the sensor on top of the engine right in front of the thermostat housing. What I need to know is, is there another coolant temp sensor some where? My Haynes manual says its the sensor by the exhaust manifold (between the sparkplugs), but RockAuto says its the one I changed.

So which is it or both? Which one sends info to the ECM?

 

[4xcrazy]

One on the side of the engine is the gauge sender, one on top is the sensor for the computer.

 

[4xcrazy]

did you put any sealer on the threads when you installed it?

 

[Slade001]

I did not put any tape on it. It just has the red sealant it came with. Is it possible that I didn't screw it in far enough? It felt like it was getting a little tight so I stopped. There are still a few threads showing.

 

[dyeager535]

Have you verified engine temp?

There are also a couple of posts here and elsewhere that list the TBI troubleshooting flow charts for all the codes, I'd suggest finding the one for your code, and running down the list in the logical pattern GM determined was best to find the issue.

The charts don't always work, but they work better than guessing.

 

[4xcrazy]

It should be a tapered brass thread setup, it'll get tighter the more you turn it, as long as it's tight and not leaking, you should be good with it.

Make sure the coolant level is up all the way too, I had that issue once, changed out some stuff, lost some coolant, I thought I refilled it enough, but after everything ran for a bit, I had a short over heat cycle until I stopped it and was able to get the cap off, not sure what happened, not sure if it was a trapped air pocket or what, not supposed to have that problem with this setup, but I really didn't add much water to it, just opening the cap and relieving some pressure seemed to help. never did it again after that.

possibly the t-stat didn't open up right away,, I dunno.

 

[Slade001]

Have you verified engine temp?

There are also a couple of posts here and elsewhere that list the TBI troubleshooting flow charts for all the codes, I'd suggest finding the one for your code, and running down the list in the logical pattern GM determined was best to find the issue.

The charts don't always work, but they work better than guessing.

Temperature was off before I changed the thermostat. Never went much above 165º. I assumed that some one, probably the PO, had changed the thermostat and put the wrong one in. But when I removed it, it WAS a 195º thermostat. Now its reading closer to the recommended 195.

 

[Slade001]

It should be a tapered brass thread setup, it'll get tighter the more you turn it, as long as it's tight and not leaking, you should be good with it.

Make sure the coolant level is up all the way too, I had that issue once, changed out some stuff, lost some coolant, I thought I refilled it enough, but after everything ran for a bit, I had a short over heat cycle until I stopped it and was able to get the cap off, not sure what happened, not sure if it was a trapped air pocket or what, not supposed to have that problem with this setup, but I really didn't add much water to it, just opening the cap and relieving some pressure seemed to help. never did it again after that.

possibly the t-stat didn't open up right away,, I dunno.

I actually DO need to top off the coolant. I noticed that after I had filled the new radiator. Just haven't made it to the store yet. I didn't think it was THAT big of a deal to be a little low. But wouldn't this code indicate that the coolant isn't getting warm enough?

 

[4xcrazy]

Could possibly just be a bad sensor. If you're verifying the actual temp is running where the t-stat regulates it at.

I noticed the other day while looking for one for my mothers truck, there a two different plug styles, not sure yet as her truck is 2000 miles away, not sure if the different plugs are between the sensor and a sender or what. one has a twin flat style pin setup, one had a vertical and one horizontal positioning pin style.

You didn't have to force the electrical plug in, did ya? maybe the wrong sensor?

 

[Slade001]

Could possibly just be a bad sensor. If you're verifying the actual temp is running where the t-stat regulates it at.

I noticed the other day while looking for one for my mothers truck, there a two different plug styles, not sure yet as her truck is 2000 miles away, not sure if the different plugs are between the sensor and a sender or what. one has a twin flat style pin setup, one had a vertical and one horizontal positioning pin style.

You didn't have to force the electrical plug in, did ya? maybe the wrong sensor?

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The one that I replaced is an oval plug, 2 wire. the one by the manifold is a single slip on wire. The connector is keyed, I just pushed it on until it clicked into place.

I'm gonna top off the coolant and keep my eye on it for a few days and see what happens. Thanks for the help and the quick replies!!!