How to wire Delphi IAT sensor into PMU16 and setup it into ECUMaster software?

PMU
1

Hi everyone,

I’m trying to use a 2-wire Delphi/GM-style IAT (NTC thermistor) as a cabin temperature reference on a PMU16 analog input (this is for my AC system logic setup), and I want to make sure I’m doing this the “correct PMU way” before I lock it in.

What I’m building

  • Purpose: cabin temperature reference (not engine IAT)

  • Sensor: Delphi/GM 2-pin IAT (NTC thermistor, typical GM curve)

  • PMU input: one Analog Input (0–5V)

Current wiring plan

  • Sensor pin 1 → PMU Analog Input

  • Sensor pin 2 → sensor ground (pin 25) / PMU ground reference

Where I’m stuck (pull-up choice)

PMU has an internal 10k pull-up option on analog inputs, but I’ve also seen people using an external pull-up resistor (sometimes 1k, sometimes other values) for thermistors.

  1. For a Delphi/GM IAT used around cabin temps (~0–40°C), is the PMU internal 10k pull-up the right choice for the best reading resolution?

  2. If an external pull-up is actually better in this case:

    • What value would you recommend and why? (1k seems aggressive to me, but maybe I’m missing something.)

  3. If I use an external pull-up, should I disable the PMU internal pull-up and only use the external one?

Temperature Wizard question (Rx value)

In the PMU Temperature Wizard there’s a field for Rx (pull-up).
4) Am I right that Rx must always match whatever pull-up resistor is actually used (internal 10k or my external resistor value)?
5) If I stick with PMU internal pull-up 10k, I should set Rx = 10000Ω, correct?

Calibration data / what I can provide

  • I can measure the sensor resistance with a multimeter at room temp (and at a couple of known temps if needed).

  • If this is a standard GM/Delphi curve, I can also use the published resistance table (e.g., typical points like 0°C / 25°C / 70°C)

  • For cabin use, do you recommend choosing the 3 wizard points around the cabin range (e.g., 0°C / 25°C / 70°C) rather than extreme points like -40°C / 0°C / 100°C?

What I’m hoping to confirm

  • Best pull-up approach (internal 10k vs external, and if external, what value)

  • Correct Wizard setup (especially Rx and which 3 points make sense for cabin/vent temps)

2

1k ohm pullup is best bet.

1k ohm to 5v pullup on GM fast IAT
Volts Temp C
0.223 150
0.280 140
0.355 130
0.452 120
0.579 110
0.746 100
0.962 90
1.238 80
1.580 70
1.988 60
2.455 50
2.953 40
3.440 30
3.878 20
4.239 10
4.512 0
4.704 -10
4.828 -20
4.905 -30
4.950 -40

3

Let say if i use the external 1k Ohm resistor as per your suggestion? How do i disable the pull-up/ pull-dowm function in the PMU software? Should i choose th 1M default?

4

Yes 1M. We can add that to the voltage calc.
Recalculated with 1k pull up and 1m pull down
0.223 150
0.250 145
0.280 140
0.315 135
0.355 130
0.400 125
0.452 120
0.511 115
0.579 110
0.657 105
0.746 100
0.847 95
0.961 90
1.090 85
1.237 80
1.400 75
1.580 70
1.776 65
1.987 60
2.215 55
2.454 50
2.702 45
2.952 40
3.198 35
3.438 30
3.665 25
3.875 20
4.066 15
4.236 10
4.383 5
4.508 0
4.613 -5
4.699 -10
4.769 -15
4.824 -20
4.867 -25
4.900 -30
4.926 -35
4.945 -40