2000 Chevrolet Malibu Question about IAT sensor

Tiny
UHSNOEBIRD
  • MEMBER
  • 2000 CHEVROLET MALIBU
  • 3.1L
  • V6
  • 2WD
  • AUTOMATIC
  • 110,000 MILES
I am having a problem with the IAT sensor, have replaced it, checked voltage while engine is running, service manual states that I should be getting 4.7 volts - 5 volts coming from the signal wire, but I am not getting it, do you think it is in the wiring or ECM or maybe some where else?

Thank You
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Thursday, January 2nd, 2014 AT 7:32 PM

17 Replies

Tiny
CARADIODOC
  • EXPERT
The confusion is in how the service manual describes how the circuit works. The sensor is fed with 5.0 volts, but you are only going to find that at the sensor if you unplug it. Doing that is going to set a diagnostic fault code. The opposite to that "open circuit" is if you grounded that wire, then you'd find 0 volts. That will also set a fault code. When the sensor is good and plugged in, you'll find between 0.5 and 4.5 volts. The higher the temperature, the lower the voltage. Anything outside of that voltage range is what triggers a fault code.

Temperature sensors have an extremely low failure rate because there is just one component in them. Almost all fault codes are a result of corrosion on the connector terminals or a corroded splice. In this case the signal wire is specific to each sensor but many sensors share a common ground wire. It isn't exactly a ground wire though. It goes to ground through the Engine Computer so the computer can monitor it for a good connection. The splice in that wire is what can corrode. Consider that a good suspect when you suddenly get multiple codes for multiple sensors. Other, non-temperature sensors share a common 5.0 volt feed wire. You'll get multiple fault codes for them when there's a break in that wire.
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Thursday, January 2nd, 2014 AT 8:15 PM
Tiny
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You are telling me to check the ground splice for corrosion. I had the plug in disconnected when I checked for voltage and was not getting the 5 volts.

Thank You
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Friday, January 3rd, 2014 AT 8:06 PM
Tiny
CARADIODOC
  • EXPERT
With it unplugged and the ignition switch on, you must find 5.0 volts on the feed wire, and you'll have 0.2 volts on the ground wire.

If you don't have 5.0 volts, there has to be a break in that wire. There's no splice in that one because that wire is specific to that sensor. When you find a little voltage there, it's getting there through some corrosion. A digital voltmeter needs almost no current to read the voltage, and that's what corrosion does. It prevents current from flowing. If you'd use a test light, which would light up dimly on 5.0 volts, you'll see it doesn't light up at all on your wire. Test lights need current to operate, and current can't get through the corrosion.

That is different than a total break in the wire. The voltmeter would not see any voltage then. You didn't say what you are getting for voltage. Is it 0 volts or something higher?
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Friday, January 3rd, 2014 AT 8:34 PM
Tiny
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One time (month ago) I got around 2.7 volts, just the other day I did not get any voltage, zero volts, I will check it again and get back to you.
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Saturday, January 4th, 2014 AT 5:48 AM
Tiny
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I got zero volts again from the signal wire and the color of it is tan, the black one is ground.
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Saturday, January 4th, 2014 AT 1:36 PM
Tiny
CARADIODOC
  • EXPERT
Dandy. You have a break in that wire between the sensor and the Engine Computer. Unplug that sensor and measure the voltage again. If you find close to 5.0 volts now, it's not a solid break as in a cut wire. You're looking for the type of break that can allow a little current to flow yet, and for this type of circuit that usually means corrosion. By far the most common cause of that is where someone poked a hole in the wire's insulation to take a reading weeks or months ago, and moisture came in and caused that corrosion. A second rather common place to look is right by the connector where the wires come out. If you tug lightly on each wire, a corroded one will act like a rubber band instead of a wire. Often the clue is the insulation will be a lighter color around the corroded spot.

The 2.7 volts you mentioned you had earlier is a proper voltage, and since it is intermittently there and not there, that also suggests a corroded spot and not cut in the wire.
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Saturday, January 4th, 2014 AT 1:56 PM
Tiny
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The 2.7 volts I got a little while back and the zero volts I am getting now is with the plug in completely disconnected from the IAT, just wanting to make sure you know that, so should I go to the computer and check to see if I am getting the 5 volts when the plug in is disconnected or what? Thanks for helping me. I appreciate it.
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Saturday, January 4th, 2014 AT 5:57 PM
Tiny
CARADIODOC
  • EXPERT
With the connector unplugged, you gotta have 5.0 volts on the feed / signal wire. Follow that one back to the computer and look for a break or corroded connector pin. I'm sorry I can't tell you which terminal that is at the computer, but those terminals are typically very reliable. Also, that 5.0 volts feeds a lot of other sensors through different terminals, so if there was a problem with that internal power supply inside the computer, you'd be getting fault codes for a lot of other sensors. I think you're going to find a break in the wire.
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Sunday, January 5th, 2014 AT 1:29 AM
Tiny
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Ok, thanks.
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Sunday, January 5th, 2014 AT 4:22 AM
Tiny
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Today, I was getting 3 volts across it while it was running and plugged in, but dorve it and light came back on again after I had removed it.
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Sunday, January 5th, 2014 AT 2:45 PM
Tiny
CARADIODOC
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I'm confused.

"but dorve it and light came back on again after I had removed it"

You unplugged it under the hood while you were driving?
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Sunday, January 5th, 2014 AT 3:55 PM
Tiny
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I am very sorry, I meant to say that I checked it while it was plugged in to sensor and then I drove it and the light came back on after it had been driven for about 20 miles but prior to the drive it was showing approx. 3 volts while it was connected to the sensor, I went through the back side of plug in to take the reading on my voltmeter. I hope that tells you better. Thanks again
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Sunday, January 5th, 2014 AT 5:35 PM
Tiny
CARADIODOC
  • EXPERT
Dandy. 3.0 volts is fine, but you're saying the Check Engine light turned on again? Did you check the codes to see if it's setting the same one? If it is, the easiest is to drive with a scanner connected so you can watch that voltage to see what it does. You can do that with a voltmeter too. You can hook it under the wiper arm or run the leads inside the car with a bunch of clip leads Actually, you need both for the whole diagnosis. If you see that voltage go to 0 volts at the sensor, and the scanner shows 5.0 volts, there's a break in that wire. If both of them go to 0 volts, that wire is grounded, and for a grounded wire to be intermittent, it typically has to be rubbing on the edge of a sharp bracket or is laying on hot engine or exhaust parts.
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Sunday, January 5th, 2014 AT 7:04 PM
Tiny
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Ok, I have a scanner and voltmeter, will try what you have said but now we have rain for the next few days, so I will wait until it is gone to do it, ok.
Again, thank you.
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Sunday, January 5th, 2014 AT 9:14 PM
Tiny
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I finally fixed my IAT problem, it was the connector at the IAT sensor, thanks for all the answers, now it's working fine.
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Monday, March 12th, 2018 AT 2:54 PM
Tiny
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I put another plug in with some additional 12 inches of wire.
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Monday, March 12th, 2018 AT 2:56 PM
Tiny
CARADIODOC
  • EXPERT
Dandy. Happy to hear you solved it. Come back to see us again.
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Monday, March 12th, 2018 AT 3:40 PM

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