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1999 Ford E-Series Van IAT reads high

Tiny
WWEST40
  • MEMBER
  • 1999 FORD E-SERIES VAN
  • V8
  • 2WD
  • AUTOMATIC
  • 88,000 MILES
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.
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Tuesday, June 29th, 2010 AT 4:35 PM

5 Replies

Tiny
BLACKOP555
  • MECHANIC
  • 10,371 POSTS
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.
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Wednesday, June 30th, 2010 AT 12:54 PM
Tiny
WWEST40
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  • 4 POSTS
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.
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Wednesday, June 30th, 2010 AT 1:25 PM
Tiny
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.
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Thursday, July 8th, 2010 AT 10:26 AM
Tiny
BLACKOP555
  • MECHANIC
  • 10,371 POSTS
Check the iat wires at the pcm first. If its getting crap in it will put crap out.
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Thursday, July 8th, 2010 AT 12:27 PM
Tiny
WWEST40
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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.
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Thursday, July 8th, 2010 AT 1:24 PM

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