Erratic readings form IAT on E38 C6 Corvette

[jfdicurt]

Hello everyone
My car has been running perfectly until we got some rare rain here in Vegas last week. All of a sudden my IAT sensor randomly jumps to max 302 degrees F. It seems worse when the car is cold - eventually it sets a MIL for IAT Sensor circuit low. We completely replaced the MAF/IAT sensor and the new one does the exact same thing leading me to believe we have a connection issue. Any ideas on this - we have sprayed and cleaned the plug up at the MAF/IAT. Is there a ground somewhere that may be dirty? Any help would be appreciated! I have posted a scan.

1283912839

Thank you thank you!

[joecar]

In quite a few cases, the IAT wires are thin and one or both break close to the connector...

with KOEO (key=on engine=off) observe IAT on the scantool while wiggling the wires behind the IAT sensor, if you see IAT being erratic then you have found the break.

[jfdicurt]

Thanks Joecar. Just went out and tried that and there were no changes when wiggling all those wires - it stayed rock solid and I jiggled them pretty strongly. I tapped on the housings, etc. I wonder if it could be a ground - or maybe where it plugs into the ECM???
Curt

[swingtan]

If the wires were broken, it'd register as an IAT of -40' (F or C). An open CCT IAT sensor is seen as a maximum cold reading. If it jumps to 302'F (150'C), that's a short CCT condition in the IAT sensor or wiring.

The wet weather may be just a coincidence, unless there have been a build up of dust on the IAT sensor which then got wet and became conductive. The only problem with that is that it needs to get down below 47 Ohms to give that reading. I'd be doing the following...


Check {A9029} and {B0188} to ensure the tune tables have not been accidentally altered.
Try a known good IAT sensor and see if the problem remains. This will indicate if it's the sensor or not.
Check the wiring for damage.


Simon.

[joecar]

Simon is right, an open causes IAT to read -40F, and a short will cause it to read high like 302F.

[jfdicurt]

Thanks guys
Definitely not the sensor. As mentioned in my initial post we put a brand new IAT/MAF sensor in two days ago. No change. Based on what you are saying it would mean the 5 volt wire is somehow shorting to its ground, correct?

[joecar]

Or the IAT signal wire is shorting to power or ground

[ if the 5V wire was shorting to ground then a fuse would blow ]

[Boost]

good informative thread!