How To Test IAT Sensor Code P0112 (1997-2004 Jeep 4.0L)

Testing the intake air temperature (IAT) sensor trouble code P0112 on your 4.0L equipped Jeep is not hard and in this tutorial I'll show you how to do it in a step by step way.

This tutorial covers quite a few 4.0L equipped Jeeps, to make sure that your specific vehicle is included, take a look at the box titled: Applies To:.

In case you're wondering: The air charge temperature sensor is the same one as the intake air temperature sensor.

You can find this tutorial in Spanish here: Cómo Probar El Sensor IAT (1997-2004 4.0L Jeep) (at: autotecnico-online.com).

Where To Buy Your IAT Sensor And Save

The IAT sensor isn't a very expensive component and just about everyone sells it. Below are links to the IAT sensor (and a few other components) that are pretty good deals:

Not sure the IAT sensor listed fits your particular 4.0L Jeep Wrangler, Grand Cherokee, or Cherokee? Don't worry, they'll make sure it fits your Jeep, once you get to the IAT sensor site, or they'll find the right one for you.

TEST 1: Checking For Shorted IAT Sensor Harness Connector Wires

A trouble code P0112 means that the PCM in your Jeep is seeing an extreme air intake temperature of 240 °F (115 °C) or higher -which of course you and I know isn't true.

There are 3 very common problems that cause a P0112 trouble code, and they are:

1. The 2 wires leading out of the IAT sensor's harness connector have shorted together (this is a very common problem).
2. The IAT sensor's harness connector is broken and the two terminals inside are shorting together (this is a very common problem).
3. The intake air temp (IAT) sensor has failed.

So, in this test step, we'll check the condition of the IAT sensor connector and the 2 wires coming out of it.

This is what you'll need to do:

1. 1

   Check that the IAT sensor harness connector isn't damaged or broken.
   
   Check that the metal terminals (of the harness connector) are not shorting together.

2. 2

   Check that the 2 wires coming out of the IAT sensor harness connector are NOT shorted together.
   
   For some reason, when these two wires short together, it happens near the plastic connector.
   
   You'll need to peel back some of the black plastic tape that's around the wires (near the plastic connector) to visually check the condition of the wires.

Let's take a look at what your test results mean:

CASE 1: The IAT sensor harness connector wires were shorted together and/or the harness connector is broken. You've found the problem that's causing the P0112 trouble code.

Repairing and or replacing the IAT sensor harness connector will solve the IAT sensor issue lighting up the check engine light (CEL) on your 4.0L equipped Jeep Grand Cherokee (Cherokee, Wrangler).

CASE 2: No problems were found with the harness connector wires or the connector itself. So far so good.

The next step is to make sure that the IAT sensor is getting power and Ground. For this test go to: TEST 2: Checking For The 5 Volts Reference Signal.

TEST 2: Checking For The 5 Volts Reference Signal

Now that you have verified that there are no problems with the IAT sensor's harness connector (or its two wires), the next step is to check that the IAT sensor is getting 5 Volts.

These 5 Volts are provided by your Jeep's PCM.

In the process of checking for these 5 Volts, we're also gonna' check the Ground reference circuit (of the sensor).

To be a bit more specific: Terminal number 1 (of the IAT sensor harness connector) is the one that feeds the IAT sensor with 5 Volts and terminal number 2 is the one that feeds Ground.

OK, to get this pot of water boiling, this is what you'll need to do:

1. 1

   Set your multimeter to Volts DC mode.
   
   If you don't have a multimeter and you need to buy one, check out my recommendation: Buying A Digital Multimeter For Automotive Diagnostic Testing (at: easyautodiagnostics.com).

2. 2

   Disconnect the IAT sensor from its harness connector.
   
   NOTE: You'll be testing for this voltage on the harness connector and not on the IAT sensor itself.

3. 3

   With your multimeter test leads, probe across the 2 IAT sensor harness connector female terminals.
   
   Your multimeter should read 4.5 to 5 Volts with the Key On Engine Off (KOEO).

Let's interpret your test results:

CASE 1: Your multimeter registered 4.5 to 5 Volts DC. This is the correct and expected test result and tells you that the IAT sensor is being fed with both power and Ground.

The next step is to check the temperature that the IAT sensor is reporting to your Jeep's PCM:

• If you have a scan tool with Live Data capability, go to: TEST 3: Checking The IAT Sensor Temperature Output.
• If you don't have a scan tool, go to: TEST 4: IAT Temperature-Resistance Chart.

CASE 2: Your multimeter DID NOT register 4.5 to 5 Volts DC. This tells you that the IAT sensor problem is due to one of two things:

1. The sensor is missing 5 Volts on terminal number 1 of the harness connector.
2.       -OR-
3. The sensor is missing Ground on terminal number 2 of the harness connector.

More than likely, this is due to an ‘open’ in the wiring between the IAT sensor harness connector and your Jeep's PCM harness connector.

Although its beyond the scope of this tutorial to check for this particular condition, you need to check the continuity of these 2 circuits with a wiring diagram to solve the IAT sensor issue lighting up the check engine light on your Jeep.