Thursday, September 16, 2021

Project-Zero: Air Temp Sensor Heck


The problem turned out to be a broken sensor.  The thermistor on the TMAP sensor was broken/missing, thus causing the ECU to run its programmed default in the event of...well...a sensor failure.

The Bosch TMAP sensor will still show a resistance value between the thermistor pins that appears to be in range even if the thermistor itself is broken/missing.
Problem: The intake temperature reading on my Emerald K6 ECU is locked at 40˚c.

Sensor: Ford combined MAP/temperature sensor, CF 331 (4S4G-9F479-AC)

Hypothesis: The voltage mapping is wrong for this sensor putting it outside of the readable ranges.


    • The Emerald K6 documentation sucks monkey and doesn't specifically address information about the electrical connection of the intake air temperature sensor.
      • Emerald simply say "Input > Air Temperature > Yes, standard Bosch or user programmable characteristic"
      • They don't offer electrical connection information.  Since the Bosch NTC sensor is a resistance type sensor I have to assume that there's an internal pull-up and I'll assume that it's a 1k Ohm resistor. ('Cause that's how things tend to be)
      • The table below is best guess/estimated values based on 5vcc in and a 1k Ohm pull-up resistor.

Since the Bosch/FoMoCo TMAP and Bosch NTC have practically the same mapping, it's safe to assume that as long I can read a resistance across the pins it should be good to use this sensorIt may be the case that there's a wiring issue in the loom that I'll need to track down but a good test will be to try with a different sensor first, since I have a Delphi sensor just chillin' out, I can plug that in to verify that the wiring is good.

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