Water thermostat... P0128?

dodgeneonzl · Post by **dodgeneonzl** » Thu Oct 23, 2008 11:54 pm

Hey guys, I'm having an engine code of P0128... which means it has something to do with the coolant thermostat... I looked at my temperature and it's about 1/4 which should means that my thermostat is working right? I also have an aftermarket water temp gauge... and it seems to corrospond correctly... like when my water temp gauge goes up, the indash water temp needle goes up too.

One thing that might be different was that because i used a "T" fitting to fit both the oem sensor and the aftermarket sensor... it seems to move everything to the right (towards battery) more... and it actually rubbed and broke off my water temp wiring connector... so what i did was i cut the whole thing off (wiring end) and attach both wires to little connectors that just plug straight into the oem sensor. Would this throw a P0128 code? I mean i can get another connector but it's 28 from the dealer for a little plastic piece and i will have clearance problem with the battery. Here's some pictures.

Post by **occasional demons** » Fri Oct 24, 2008 12:22 pm

Possibly since you have the sensor spaced away from the head, it is taking too long to heat up. ?

Paul56 · Post by **Paul56** » Fri Oct 24, 2008 12:46 pm

Hmm, your stock gauge needle is sitting a little lower than mine does as operating temperature.

Mine normally sits just a hair above the first mark while yours appears to be *several* hairs below.

dodgeneonzl · Post by **dodgeneonzl** » Fri Oct 24, 2008 2:55 pm

It doesn't take too long to heat it up... it seems like a normal heat up time for me... Usually if i parked the car at rest for a while it will be at the 1/4 mark... but then when i started driving the car, it usually cools down to that mark... sometimes even lower... but then again i have an carbon fiber srt hood... so that might direct some of the air into the engine bay when driving?

But still... does the lower temperature causes the code though??

Danteneon · Post by **Danteneon** » Fri Oct 24, 2008 4:58 pm

I believe that you may be getting this code because you have an additional sensor on the OE circuit. It may be that the PCM is reading both signals and it is very confused.

Simple way to test it. Remove the aftermarket sensor from the circuit and clear the code. See if that helps.

dodgeneonzl · Post by **dodgeneonzl** » Fri Oct 24, 2008 5:10 pm

Might be it... do you think it'll be good enough just removing the wiring that's supplying the power to the t'stat would be good enough or removing the whole thermostat? I mean removing the whole thermostat is gonna be a pita...

and by only removing the wire, it should just be like a regular pipe right?

Danteneon · Post by **Danteneon** » Fri Oct 24, 2008 5:11 pm

Don't remove anything mechanical, just remove the electrical portion of the aftermarket set-up from the OE harness.

dodgeneonzl · Post by **dodgeneonzl** » Mon Oct 27, 2008 7:16 pm

Alright, so i tried taking out the wires... but the code's still there. I mean, the t'stat should be good right? since it "is" getting a temperature reading? And the temperature seems about right along with my aftermarket water temperature t'stat. So any other ideas? because i really wanted to get this to work and i don't feel like taking the whole thing off..

Besides... i'm not sure where else i can put the t'stat except at the back of the block which is gonna be a pita to get to. Thanks!

*edit*
wait... hang on...

you said take out the circuit and then "clear" the code? that would take a OBDII reader i believe? I only take out the circuit... i didn't use the OBDII tool, i get the code by turning it on and off 3 times and looking at the cluster.

Post by **occasional demons** » Mon Oct 27, 2008 9:45 pm

Back up a minute. Do you have the two wires from the oem sender just extended with the red wires, or are they tied into the aftermarket sender wire (single one held on by the nut)?
The OEM sensor has two senders in it. One is to turn the fan on and off and the other is for your temp gauge.
Or do you have a totally seperate circuit for the aftermarket gauge sender? (Which is what I was thinking.)
But if it is the latter you may also have to attach a ground wire somehow, as the tape from all the connections may be compromising the ground to the head.
If it was me, I would tee into the heater tube hose for the aftermarket gauge with a ground soldered onto the tee for the sender. This is what I did on the 3.0 in my Raider, and it seems to work fine. Someone correct me if I'm wrong, but I believe the coolant runs through the heater tubes as long as the engine is running. you just need to determine which one is the "hot" side.
I know it's not what you had in mind, after going through all that trouble but it may be the "better" soultion.
The fun of trail and error. Believe me I've reworked plenty of stuff, but it's how we learn. If this stuff worked perfect the first time, everytime, we would have gotten bored with it long ago. Granted, on some things we would be much happier...

dodgeneonzl · Post by **dodgeneonzl** » Tue Oct 28, 2008 4:21 am

Hey, yeah, it's a complete separate sender wire... I thought about the ground... but it seems to work fine which is why i thought the ground is working, unless the engine code appears becaues of the insufficient grounding of the wire?

Also, occasional daemon, is there any how to as to tapping into the heater hose? Or maybe a kit?
Also, i heard that someone tapped into the radiator hose instead too... but if you know where i can get a how to for that, let me know! Thanks!

Post by **occasional demons** » Tue Oct 28, 2008 8:13 am

What I did was get a brass tee, 1/2" npt IIRC, two 11/16" hose barbs (I think thats the diameter of the heater hoses, could be 5/8") Then cut the hose and put the tee w/barbs inline and use the 3rd opening to put the sender in. But you still need to attach a ground to the tee, by either soldereing one on or clamping somehow.