Aux V Signal issues

[Carlos Iglesias]

My M4 has Aux V setup for EMAP sensing and I'm having trouble with the input.

After an engine rebuild, I noticed that the sensor abruptly doubled it's output during the middle of the first post-build engine cranking. The new values were obviously wrong, at least at ambient pressure. I replaced the sensor with a new Honeywell (HW) 0-50 PSIg pressure sensor (p/n ST050PG1SPCF). However, after updating the Sensor Cal Table with the new entries, the Aux V reading was still incorrect. Troubleshooting ensued:

1) Auv V A/D count is 602 (2.94v) when the HW Sensor is normally connect at the ECU-to-engine harness.
2) Aux V reads 4.4v at the ECU (pin #18) without anything connected to it (i.e. ECU connector pin pulled.)
3) HW sensor signal correctly reads .51v when the sensor signal pin is not connected to ECU harness (i.e. sensor signal pin -> multimeter -> chassis gnd) but 0v and 5v for the sensor are sourced from the ECU.

Both the MoTeC seminar printout and the recent Webinar indicate that the analog (e.g. Aux V) signal(s) should read 0v when the sensor is not connect. Yet I have also read on this Forum that the analog signal input to the ECU "floats" and therefore could indicate high values. I'm a bit confused, and so will very much appreciate any further troubleshooting recommendations for getting Aux V reading correctly.

Cheers, Carlos