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

TEST 3: Checking The IAT Sensor Temperature Output

If you've reached this point, you have:

One: Checked the condition of the IAT sensor harness connector and the 2 wires coming out of it for shorts (TEST 1).

Two: Verified that the IAT sensor is being fed 5 votls and Ground (TEST 2).

The next step is to see the IAT sensor's temperature output with a scan tool in Live Data mode. Now, if you don't own a scan tool, don't panic. You can use a multimeter to check for the IAT sensor's temperature output by checking its resistance. For this test, go to TEST 4.

NOTE: To get an accurate test result, the following scan tool test steps require that your Jeep's engine be completely cold.

OK, this is what you need to do:

1. 1

   Connect your scan tool to your Jeeps diagnostic link connector (DLC).

2. 2

   Once it has powered up, go to its Live Data mode.
   
   If you don't have a scan tool and you need to buy one, check out my Actron CP9580 Scan Tool Review

3. 3

   Scroll down to the PID labeled IAT (°F)

   1. In case you're wondering, PID stands for: Parameter ID (ID = Identification).
4. 4

   The scan tool should register a temperature that should be within ±10 °F of ambient temperature (if all is normal).
   
   So let's say that it's 50 °F outside, then the IAT sensor PID should register something between 40 to 60 °F.
   
   Now, since you're here because you have an IAT sensor diagnostic trouble code (DTC), more than likely you'll see one of the following:

   1. -40 °F (-40 °C) or colder.
   2. OR 284 °F (140 °C) or hotter.

Let's interpret your test results:

CASE 1: Your scan tool shows a -40 °F (-40 °C) or colder reading- This extreme cold temperature reading clearly indicates that there's a problem with the intake air temperature sensor.

If you have:

1. Confirmed that there are no problems with the harness connector and its 2 wires.
2.    -AND-
3. Confirmed that the IAT sensor is being fed power (5 Volts) and Ground.

Then you can confidently assume the IAT sensor has failed and needs to be replaced.

CASE 2: Your scan tool shows a 240 °F (115 °C) or higher reading- This extreme hot temperature reading clearly indicates that there's a problem with the intake air temperature sensor.

This temperature reading also confirms that the diagnostic trouble code P0112 (IAT Sensor Circuit Low Voltage) that you retrieved from the PCM's memory is right on the money.

If you have:

1. Confirmed that there are no problems with the harness connector and its 2 wires.
2.    -AND-
3. Confirmed that the IAT sensor is being fed power (5 Volts) and Ground.

Then you can confidently assume the IAT sensor has failed and needs to be replaced.

CASE 3: Your scan tool shows a temperature reading that's ±10 °F of ambient temperature- This test result tells you that at the moment the IAT sensor is functioning correctly.

But, since you still have a DTC P0112 or P0113 registered on your PCM's memory, I recommend clearing the diagnostic trouble code (DTC) and road testing your vehicle to see if the code comes back.

If it does, repeat this test once more.

TEST 4: IAT Temperature-Resistance Chart

If you don't have a scan tool that has Live Data capability, then the next best thing (to confirm trouble code P0112) is to see what the resistance of the IAT sensor is.

Now, to give you some specifics on how to do this and what exactly you're looking for (with this test), the purpose of this resistance test is to see if the IAT sensor's resistance is between 340 to 0 Ωs. Why?

Because: One: a trouble code P0112 means that your Jeep's PCM is seeing an IAT sensor temperature output of 240 °F (115 °C) or hotter. Two: If the sensor is fried (and thus reporting this extremely hot temp), then its internal resistance will be between 340 to 0 Ω.

So, using the temperature to resistance chart below, you can test the IAT sensor and find out if its truly fried (and needs to be replaced) or not.

Temperature / Resistance
°F	°C	Ohms (Ω)
248 °F	120 °C	370-410 Ω
230 °F	110 °C	480-540 Ω
212 °F	100 °C	640-720 Ω
194 °F	90 °C	860-970 Ω
176 °F	80 °C	1,170-1,340 Ω
158 °F	70 °C	1,630-1,870 Ω
140 °F	60 °C	2,310-2,670 Ω
122 °F	50 °C	3,330-3,880 Ω
104 °F	40 °C	4,900-5,750 Ω
86 °F	30 °C	7,370-8,750 Ω
77 °F	25 °C	9,120-10,880 Ω
68 °F	20 °C	11,370-13,610 Ω
50 °F	10 °C	17,990-21,810 Ω
32 °F	0 °C	29,330-35,990 Ω
14 °F	-10 °C	49,250-61,430 Ω
-4 °F	-20 °C	85,850-108,390 Ω
-40 °F	-40 °C	291,490-381,710 Ω

NOTE: If your test results indicate a resistance value that closely matches the ambient temperature of your surroundings, then this test result tells you that the IAT sensor is OK. This also tells you that the either the problem is intermittent or the problem isn't with the IAT sensor itself.

More Jeep 4.0L Test Tutorials

If this tutorial was helpful/informative, you can find a complete list of tutorials here: Jeep 4.0L Index Of Articles.

Here's a sample of the tutorials you'll find there:

• How To Test Trouble Code P0135 (1996-2000 Jeep 4.0L).
• How To Test The MAP Sensor (1997-2003 Jeep 4.0L).
• Jeep PWM Fan Relay Test Troubleshooting An Overheating Condition.
• How To Test The Crankshaft Position Sensor (1994-1996 4.0L Jeep).