bad temperature readings on scan tool

[jeepster]

I got a Vident scan tool, as it works with old ALDL. Playing around with it, the live data temperature readings look wrong. Firstly the IAT was constant 76 degrees C. I have a spare sensor, so plugged that in, and it reads 83 degrees. But then looking at IAT voltage, that was 2.25 volts. From workshop manual, that would be about 55 degrees, so I guess the calibration is wrong in the Vident software.
Secondly, engine coolant temperature reading is minus 40. That would suggest open circuit. ECT voltage reads as zero. But that should trigger an error code, and the only code is 76 (short term fuel trim left-right difference). Unplugging the coolant sensor turns on the radiator fan, so there isn't an open circuit.

 

[shane_3800]

Meh it's a VR/VS if the temp gauge reads fine on the dash it's good.

 

[Immortality]

Not really, there are 2 sensors and the dash sensor is only for the driver, the other sensor is used by the PCM and is the critical one.

I'd question the supplier about the scan tool accuracy? Does the scan tool have options to select different vehicles?

 

[Lex]

Does the scan tool have options to select different vehicles?

Hi
I have the same scan tool. It does have the option to select different vehicles & motors, manual or auto.

 

[jeepster]

Not really, there are 2 sensors and the dash sensor is only for the driver, the other sensor is used by the PCM and is the critical one.

I'd question the supplier about the scan tool accuracy? Does the scan tool have options to select different vehicles?

This only has Holden pack installed. You select the year, then the model after that. Also does the Opel/Daewoo cars which Holden sold. I would guess they pirated the Tech1/2 cartridges to get all the functions. There is a complaint page on the manufacturers website. I will try it out on another VS to confirm it is bad before contacting them.

 

[_R_J_K_]

I will try it out on another VS to confirm it is bad before contacting them.

Are you doing this when the car is hot and running in closed loop mode?

 

[jeepster]

Are you doing this when the car is hot and running in closed loop mode?

I have tried with the engine running for several minutes and with engine stopped.
I don't see that as relevant: the PCM will monitor the ECT to decide when it changes to closed loop mode.
So I tried it in another VS II V6 automatic. The IAT looks plausible there, but ECT is still -40 degrees.

 

[_R_J_K_]

I have tried with the engine running for several minutes and with engine stopped.
I don't see that as relevant: the PCM will monitor the ECT to decide when it changes to closed loop mode.
So I tried it in another VS II V6 automatic. The IAT looks plausible there, but ECT is still -40 degrees.

It will be relevant depending on how the PCM has been architected and built by GM/Delco. For example, when you turn the car to accessories and the fuel pump primes, the pump primes through the use of a crank signal in the ECU even though the engine is not turning, not because the ECU is directly telling the pump to run if that makes sense. A -40 degree ECT could just be normal operation until the car is running in some other state (which would explain why it wouldn't throw a code), i.e. the ECU could use this value (if it is in fact a totally zero value, or a multiplier or offset based value) to dump fuel into the engine based on a cell in a fuel table while it's cold. Why might it do this if it does? My guess would possibly be because this ECU has it's roots in the mid 80s.

You might be better off asking this question at the PCM Hacking forums, particularly with how this ECU uses value offsets and multipliers extensively in different scenarios.