CLT and IAT sensors reading high

[Bilious Bob]

Hi,

I'm banging my head against the wall trying to get my temp sensors working correctly.

I am working on a conversion using a 3.57 board/msii/2.89 with the relay board and cable from DIYAutoTune.. I was originally going to use my stock bosch sensor for CLT and a Pontiac Sunfire sensor for IAT, so I very carefully measured temp/resistance for as wide a range as I could (basically 0C to 99C) and put my readings into the thermal sensor calibration window...only to have both CLT and IAT reading way high. Eg. at 30C, CLT reads 50C in megatune. So I thought maybe there was an issue with the sensors, and ran to the JY to pick up a couple of GM sensors. After first checking them for functionality using a ohmmeter, I plugged them in and re-config'd for standard GM values...only to have them read ~20C high @ 30C.

So then I re-flashed the MS unit. No change whatsoever.

I have verified that R4 and R7 are both stock. The only mods I made to the MS was for using a sink-to-ground hall sensor for ignition. I actually un-did the mods in *just in case*, which of course had no effect either.

As a last resort, I disconnected everything else from the MS unit...literally, it is connected to 12v, ground, and IAT. No effect.

Any ideas? Any thoughts on where I should begin to troubleshoot?

Thanks much in advance,

Aaron

[Bilious Bob]

I forgot to add that I have verified that both CLT and IAT terminals also show voltage consistent with vref (4.93v), and I've checked continuity in the relay cable (as well as a visual of the ends under the shields).

[Matt Cramer]

Could you post exactly what values you've used for the calibration, including bias resistor values?

[Bilious Bob]

Could you post exactly what values you've used for the calibration, including bias resistor values?

Sure. Bias resistors on the board are both marked 2491.

In tunerstudio, I'm using the standard GM sensor setup:

Bias resistor value: 2490
-40C 100700 ohms
30C 2238 ohms
99C 177 ohms

and I did test the sensor, though not at these specific temps. At 70 degrees F, the sensor was pretty much spot-on at 3400 ohms.

Thanks for the help,

Aaron

[Matt Cramer]

Try unplugging the sensors. What does the temperature read then?

[Bilious Bob]

Hmmm. With both sensors unplugged, I get 100C for coolant and 39C for air. I pulled the leads from the relay block, so it's jut the cable connected to the relay with nothing else connected, and I still get 100C and 39C. JUST to be sure, I reflashed again and re-ran the thermistor calculation tool with the GM values.

[Matt Cramer]

Looks like it's defaulting to a safe reading - do you get the same reading when you short the IAT and CLT terminals to ground?

[Bilious Bob]

yup, sure do. 100C and 39C when shorted.

temp does fluctuate with the sensor attached - it's just way off. i've tried the gm sensors as well as a few other sensors i had laying around (after measuring/calibrating them in tunerstudio) with the same results.

i'm really confused at this point.

[Bilious Bob]

Just for full disclosure, these are the mods done for the sink-to-ground hall sensor (works great):

Replaced D1 & D2 with jumpers
Removed C12 and C30
Removed jumper from XG1 and XG2
Removed jumper from JP1
Connected XG1 to JP1-pin2
Connected +5v from proto pad to JP1-pin3

[V12Buick]

I am having the same problem with my CLT sensor.
It's a standard GM sender unit and I have also checked the resistances at near freezing(ice water) and at approx 30°C and the resistances are close to what they should be. I have even compared the resistances to the Manifold Air Temperature sensor unit and they are almost identical, however the MAT will provide a reading of approx 26°C but the CLT will read 77°C.
The ECU that I am using is a preassembled MS II.
Any assistance in resolving the issue would be appreciated.

Another issue that I have, which may or may not be associated, is that whilst the real time display recogises that TPS and I can watch it move from 0 to 100%, when I am trying to start the engine (it wont idle properly yet) opening the TPS has no effect at all. It almost appears as if the ECU does not recognise it being operated

[Matt Cramer]

yup, sure do. 100C and 39C when shorted.

temp does fluctuate with the sensor attached - it's just way off. i've tried the gm sensors as well as a few other sensors i had laying around (after measuring/calibrating them in tunerstudio) with the same results.

i'm really confused at this point.

Could you try bench testing it with the sensor in boiling and ice water? Take the lid off and check the voltage at the processor pins; let me know what you find on each circuit.

[V12Buick]

After checkingthe resistances of the CLT and MAt sensors I checked the voltages against the Vref and across the terminals of the sender units. This was done across the terminal block of the relay board.
Using the terminal block pin numbers I was able to measure the following.
#12 (Vref) to #16 (MAT) 2.94 V
#12 (Vref) to #17 (MAT return ) 4.95 V
#12 (Vref) to #18 (CLT) 4.95 V
#12 (Vref) to #19 (CLT return) 4.95V
#12 (Vref) to #20(EGO) 4.95 V

#16 to #17 2.01 V
#18 to #19 0.0 V
So there appears to be a problem with the the CLT circuit. I have checked the wires to and from the sensor and there appears to be no problem. However I am using a 4 wire EGO sensor and the return from this sensor is connected to #19 pin as well. Could this be the problem? I removed it from #19, but it did not make any difference.

When checking the resistances of the CLT and MAT sensors at the sensors themselves they were quite close to each other, however with the ECU powered up I also checked the resistances across #16 & 17 and across #18 & 19 and they were significantly different. i.e at the senders they were both about 1800 ohm at the relay block the MAT was about 800 ohm and the CLT was still around 1800 ohm.

[Matt Cramer]

The O2 sensor is not the problem - sounds like something in the CLT circuit is shorted to ground.

[V12Buick]

I will check the wiring to and from the CLT sender and the relay board, but as I bought a Pre-assembled board MS II where should I start to check the ECU circuit?

[Matt Cramer]

I will check the wiring to and from the CLT sender and the relay board, but as I bought a Pre-assembled board MS II where should I start to check the ECU circuit?

On the Stimulator; see if the CLT responds to turning its adjustment pot.

[twofouroh]

Does the ground from pin 19 need to be seperated from the other ground wires? My kit from DIY only came with 2 big ground wires, so I wired 19 in with the other ground pins near it.

[Matt Cramer]

Does the ground from pin 19 need to be seperated from the other ground wires? My kit from DIY only came with 2 big ground wires, so I wired 19 in with the other ground pins near it.

A separate sensor ground is better (our newer harnesses have changed the ground wire setup) but either way should work.

[V12Buick]

I did some checking and found a couple of broken solder joins in my wiring loom between the ECU and the relay board.
Once resoldered everything now seems to be working well, thanks for your help