How To Test: P0112 OBD II Trouble Code (Honda 2.2L, 2.3L)

OBD II trouble code P0112 IAT Sensor Circuit Low Voltage usually points to one of two things, either a failed intake air temperature (IAT) sensor or a short in the sensor's wiring.

In this tutorial, I'm gonna' go into the specifics of why your Honda sets a P0112 trouble code and, more importantly, I'm gonna' show you how to test the IAT sensor in a step-by-step way.

P0112 Basics You Need To Know

The IAT sensor's job is to sense and report the temperature of the air entering the engine to the fuel injection computer.

The computer uses this information, along with several other sensor inputs, to fine tune the amount of fuel that needs to be injected into your Honda's engine.

To go into a few more specifics, if the incoming air is warm, the PCM injects less fuel. If the incoming air is colder, the PCM needs to inject more fuel.

So, when a code P0112 lights up the check engine light (CEL) on your Honda's instrument cluster, the PCM is letting you know that there's a major problem with the temperature value that the intake air temperature sensor (IAT) is reporting to it.

Specifically, that the IAT sensor is reporting that the temperature of the air entering the engine is around of 302 °F (150 °C) or higher. Yeah, that's pretty hot!!

In a nutshell, this is how the intake air temperature (IAT) sensor works:

1. The intake air temperature (IAT) sensor is a 2 wire sensor.
   • One wire (circuit) supplies power. This power is in the form of 5 Volts DC (which come from the PCM).
   • The other wire (circuit) supplies Ground. The PCM supplies this Ground internally.
2. The IAT sensor is a resistor (thermistor). Its resistance changes in response to changes in the air's temperature.
   • The cooler the air, the higher the resistance of the IAT sensor.
   • The warmer the air, the lower the resistance of the IAT sensor.
3. When the 5 Volts pass through the intake air temperature (IAT) sensor, the resistance of the sensor produces a voltage drop. This in plain English means that only a certain amount of the 5 Volts are let through to the Ground wire.
   1. The cooler the air is, the less voltage is let thru' onto the Ground wire (due to the IAT sensor's higher resistance).
      • The PCM translates this higher voltage drop into a colder temperature value.
   2. The warmer the air, the more voltage is let thru' onto the Ground wire (due to the IAT sensor's lower resistance).
      • The PCM translates this lower voltage drop into a warmer/hotter temperature value.

So, when a P0112 IAT Sensor Circuit Low Voltage is stored in the PCM memory, the PCM is letting you know that the intake air temperature (IAT) sensor is reporting an extremely low voltage drop (think IAT sensor wires shorted together).

The PCM interprets this condition as an extremely hot air temperature (above 200 °F).

When your Honda's fuel injection computer (also known as the PCM = Powertrain Control Module) sets a P0112 IAT Sensor Circuit Low Voltage diagnostic trouble code (DTC), it's because the PCM sees the intake air temp (IAT) sensor reporting a temperature of 302 °F (150 °C) or higher.

Symptoms Of A P0112 Diagnostic Trouble Code

The PCM, in your Honda, uses the input from the IAT sensor to know the incoming air's temperature. With this info, it can inject the proper amount of fuel into the engine.

When the IAT sensor fails or there's a problem with its circuits (wires), your Honda isn't gonna' run optimally.

The symptoms of a bad intake air temperature (IAT) sensor are:

1. Check engine light (CEL) is on.
2. DTC P0112 is present.
3. Won't pass the state mandated emissions test.
4. Gas mileage will suffer.
5. Rough idle.
6. Hard start and/or extended cranking time.
7. Black smoke coming out of the tailpipe.

Let's find out what are the common causes of a P0112 DTC, in the next subheading.

Common Causes Of A P0112 Trouble Code

Here are the most common causes of a P0112 diagnostic trouble code (DTC):

1. Bad intake air temperature sensor.
2. Intake air temperature sensor wires have shorted together.
   • This is usually due to human error (like when the engine is replaced and the IAT sensor's connector or wires are damaged).
3. Bad PCM (Powertrain Control Module = Fuel Injection Computer).
   • This is very rare, but it does happen.

With this basic info under our belts, let's turn the page and get testing!