Coolant Temperature Sensor not reading on MSPNP2
 

After installing mspnp2 on my 96 stock engine. I have ran into a few problems I have not had any luck resolving or finding in the forums. Loaded the base maps and did some tuning to get it to run. Megasquirt does not read my coolant temperature sensor (CLT). It reads 180F and does not move even when it overheats based on the dash gauge. Here is what I`ve tried so far:

1. Calibrating the sensor based on information on DIY, MT.Net and M.Net. Set the resistor values based on the RX7_CLT ( S4 & S5) and the bias resistor to 1250,1550,2490,4890 Ohms to try and trouble shoot.

2. Replaced the sensor just in case, still nothing. When the OEM ECU was in I never had an overheating problem with fan engagement.

3. Opened the mspnp2 up to see if the R7 resistor was missing (got the MS used) everything is untouched. This was from my understanding something for MS1.

4. Measured the voltage at the sensor plug, got nothing, so I`m thinking it is a setting issue...

I have set the fans to always be on to avoid overheating, but want to get the MS and temperature to work together. Anyone had anything similar happen? Something they suggest I look into?

There is no voltage, the temp sensor is just a variable resistor, then it gets turned into a voltage inside the ECU. Check continuity between IAT connector and ECU connector, for both the signal wire to signal input pin, and from ground wire to sensor ground pin.

Thanks for the response.

I tested the CLT sensor wiring. Both lines work / have continuity ( signal & ground ) from the connector to the ecu. Do I test the IAT too? Still have the stock AFM.

Anyone?

This is incorrect. The coolant sensor is a thermistor but the ecu can't measure a resistance change directly. The sensor is part of a voltage dividing circuit. When the resistance of the sensor changes the voltage out of that circuit changes. The voltage change is what the ecu is able to read.

What's important about this for the OP is that there should in fact be voltage at the connector.

The TPS sensor doesn

The TPS sensor doesn`t give a good reading either even after calibrating it manually and on tunerstudio. Reads 97% closed 99% open. Could this be related?


Since I have continuity could this still be a setting issue?


Should I use a custom inc. file or find the code for the sensor?


Could the basemap be wrong? I have 3.3 version with the basemap MS2E v3.3.1a MSPNP2-MM9697

Measure the voltage on pin 3F of your ecu. Voltage should vary between 0 and 5V when changing throttle position. If it doesn't, something is wrong with your tps sensor or its wiring.

Both the tps and the coolant sensor rely on the same 5v reference output from the ecu. Check for voltage at pin 3I with the key on. Should be a green/white wire.

Thank you all for your input.

I will test the wirings out and try to source a good TPS sensor to swap out.

Will post results as soon as I can.

I tested the wirings for the TPS and they came out good. Did this back when I was testing the CLT.

I got used TPS to see if mine was bad after getting wierd reading from my multimeter. Same thing so both TPS are good.

I measured the voltage when on in the TPS and I dont get any. Also tried to calibrate the TPS and still at 98-99% for open and closed.

Was reading and saw MS3 had a TPS safety enabled in CANBUS, but doubt it applied to MSpnp2 specifically if a jumper needs to be jumped? I did not see or read anything about it. Car runs the same with or without the TPS, but the CLT is important for getting the car to run right.

At this point I'm wondering if there is anyone near Houston,TX that could take a look?

So 3I showed 5v with the key on?

3F varied voltage with throttle position?

No voltage on the tps and clt connectors.

I'm not convinced it is not a grounding issue. Does anyone know where they ground to in the engine bay?

Read that the clt, iat and tps share the same ground. Is this correct?

If you aren't getting 5v to one of the pins on those sensors then it isn't a ground issue.

For the third time, do you have 5v at 3I at the ecu. Green/white wire

3I does have 5V measure from the ECU ground wire to chassis and 3I.

Also there is continuity between the ECU ground wire and 3O.

Dont know the circuit well enough to say 3I should work with 3O because it does not.

You have 5v at 3l but not at the sensors?

That is correct. No voltage at sensors and yes right out of the ecu. 3I.

It seems that I need to find where the clt and tps ground to as there is not a complete circuit.

Nope.

If you unplug the coolant sensor and don't have 5v with the key on at either pin, but you have 5v out of the ecu that does not point to a ground issue. It means you have a break in the wire somewhere between the ecu and the sensor.

So thanks to the suggestions to test the 3I and seeing that it had 5V I retested the continuity and found that it has continuity.

So I realized that I was testing the voltage using the tps harness ground instead of engine and concluded that the grounding wire is the culprit. Using the engine ground I now see 5v at the tps sensor connector.

Will look into where the ground is. Noticed that the ground wires in the front of the throttle body look corroded.

did you fix this issue?
i have the same problem mega squirt isn’t reading the clt or iat sensor. I replaced the coolant sensor with an oem one with a new pigtail too.