1999 Ford E-Series Van IAT reads high

1999 FORD E-SERIES VAN
88,000 MILES • V8 • 2WD • AUTOMATIC
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WWEST40
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Autotap scan tool indicates IAT to be 217F to 247F.

New MAF/IAT installed, same.

Wiring checks out okay from MAF/IAT module to computer connector.

Voltage output from IAT is about 2.5 volts.

No codes, just that MIL will NEVER run to completion.

Computer detects open IAT when I open the circuit.

IAT signal lead reads about 3.3 volts with circuit open.
Jun 29, 2010 at 4:35 PM
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BLACKOP555
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measure the resistance of the new sensor with it coldthen warm what do you have?

sounds like you have low resistance reading the high temp. you should be check to make sure the wires are not shorted together in the harness somewhere.
Jun 30, 2010 at 12:54 PM
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WWEST40
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Autotap has a flaw...

Reporting IAT temperatures in the range of 217F to 247F, 338F open circuit.

According to the Ford shop/emissions manual the IAT sensor is perfectly fine, ~2.5 volts and 28K ohms with OAT ~65F, and 3.5 volts open circuit.

Hours troubleshooting a non-existent problem plus $120 for a new rebuilt MAF/IAT.
Jun 30, 2010 at 1:25 PM
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WWEST40
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Looks as if I was wrong about AutoTap.

The PCM, Powertrain Control Module, "throws" no codes just that the drive cycles will not clear the MIL and that is apparently due to the IAT temperature being out of range, too high, 217F to 247F.

TPS connector has full 5 volt reference and I have checked the wiring harness very thoroughly along with the IAT resistance, 28K ohms at 82F OAT.



I'm now guessing the PCM needs replacing...

Thoughts..??

PCM's IAT input pin reads 4.8 volts with the MAF/IAT connection open, ~2.2 volts connected.
Jul 8, 2010 at 10:26 AM
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BLACKOP555
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check the iat wires at the pcm first. if its getting crap in it will put crap out..
Jul 8, 2010 at 12:27 PM
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WWEST40
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[quote:e007f92e5f="blackop555"]check the iat wires at the pcm first. if its getting crap in it will put crap out..[/quote:e007f92e5f]

I actually opened the PCM and measured the IAT resistance from a point on the circuit board, also measured voltage at that same point, 4.8 volts open circuit, 2.7 volts IAT plugged in.

Off to CARDONE.
Jul 8, 2010 at 1:24 PM