How to Test a P1122 Diagnostic Trouble Code (Honda 2.2L, 2.3L)

OBD II trouble code P1122 TP Sensor Signal Higher Than Expected indicates that the throttle position sensor (TPS) is reporting a continuous high throttle plate angle when other sensor input (to the PCM) indicates the opposite is happening.

Troubleshooting the throttle position sensor (TPS) to see if it has failed and thus causing the P1122 DTC is pretty easy. In this tutorial, I'll show you how using a multimeter and in a step-by-step way.

Here are the contents of this tutorial at a glance:

  1. P1122 Basics You Need to Know.
  2. How the Throttle Position Sensor (TPS) Works.
  3. Symptoms of a P1122 Diagnostic Trouble Code.
  4. Common Causes of a P1122 Trouble Code.
  5. START HERE: Troubleshooting DTC P1122.
  6. TPS TEST 1: Testing the TPS Voltage Signal.
  7. TPS TEST 2: Verifying TPS Has Power.
  8. TPS TEST 3: Verifying TPS Has Ground.
  9. Where to Buy Your TP Sensor and Save.
  10. More Honda 2.2L, 2.3L Test Tutorials.

P1122 Basics You Need to Know

Your Honda's PCM needs to know the throttle angle to keep your vehicle running and performing optimally.

It's the throttle position sensor's job to measure the throttle angle (throttle angle = how much the throttle plate opens or closes) and then relay this info as a DC voltage signal via the TP sensor connector's middle wire.

The PCM then uses throttle position information to either inject more or less fuel and a host of other things that make your Honda run or keep running.

To give you a few more specifics:

  1. As you step on the accelerator pedal,
    1. The TP sensor measures the increasing throttle angle and sends a corresponding voltage signal to the PCM.
    2. The fuel injection computer injects more fuel.
  2. As you let your foot off the accelerator pedal,
    1. The TP sensor measures the decreasing throttle angle and sends a corresponding voltage signal to the PCM.
    2. The fuel injection computer injects less fuel.

This makes the throttle plate angle information a critical part of the computer's fuel injection, ignition system, automatic transmission control strategy (to name a few).

Now, when the PCM sees the TP sensor producing a high voltage that indicates a closed throttle plate even though other sensor inputs indicate otherwise... it sets a code P1122 TP Sensor Signal Higher Than Expected and lights up the check engine light (CEL) on your Honda's instrument cluster.

How the Throttle Position Sensor (TPS) Works

How to Test a P1122 Diagnostic Trouble Code (Honda 2.2L, 2.3L)

Your Honda's throttle position sensor needs power and ground to function and these are fed to the sensor via 2 of the 3 wires that connect to it.

The third wire (which is the middle one) is the one that returns the signal, the TP sensor creates, to the PCM.

To better understand how we're gonna' test the throttle position sensor (TPS), in this tutorial, I'm going to briefly describe each wire's job and how the sensor works.

Don't worry... it's nothing too technical and it's all in plain English:

  1. The TP sensor is a 3 wire sensor.
    1. Wire labeled with the number 1.
      1. Feeds ground to the TP sensor.
      2. Ground is provided by the PCM (internally).
    2. Wire labeled with the number 2.
      1. Feeds the throttle angle voltage signal to the PCM.
      2. This voltage signal increases or decreases depending on throttle angle.
    3. Wire labeled with the number 3.
      1. Supplies power to the TP sensor.
      2. In the form of 5 Volts DC and is supplied only with Key On Engine Off (KOEO) or Key On Engine Running (KOER).
      3. The PCM supplies these 5 Volts DC.
  2. The TP sensor is a potentiometer. Its resistance changes in response to changes in the throttle plate's angle.
    1. With throttle closed, a small voltage is create and sent to the PCM.
      1. At closed throttle the TP sensor outputs about .5 Volts DC.
    2. With throttle open to wide open, a bigger voltage is created and sent to the PCM.
      1. At wide open throttle the TP sensor outputs about 4.5 Volts DC.

REMEMBER: The key to diagnosing the TP sensor is to know that at a lower throttle (angle), like at closed throttle, it produces a low voltage signal of around .5 Volts DC.

As the throttle plate position increases (as you step on the accelerator pedal and accelerate the engine), the .5 Volt TP signal starts to increase. At wide open throttle, the TP sensor will output about 4.5 Volts DC.

With this bit of information, let's move on to the next subheading...

Symptoms of a P1122 Diagnostic Trouble Code

Throttle angle information is critical for the performance of your Honda... so when the PCM receives a TP signal that doesn't square with actual engine operating conditions... you'll feel it.

You'll see one or more of the following symptoms:

  1. Check engine light (CEL) shining nice and bright.
  2. DTC P1122 is present.
  3. Your Honda fails the state mandated emissions test.
  4. Bad gas mileage.
  5. Hard start and/or extended cranking time (after shut off).
  6. Black smoke coming out of the tailpipe.
  7. Hesitation when accelerating your Honda.

Let's find out what are the common causes of a P1122 DTC, in the next subheading.

Common Causes of a P1122 Trouble Code

The 3 most common causes of trouble code P1122 are:

  1. A bad throttle position sensor (TPS).
  2. A broken TP sensor connector.
  3. A problem in the sensor 3 wires. Specifically, a short in one of them.

Although extremely rare for this to happen... a bad PCM can also cause a false P1122 trouble code.

In this tutorial, I'll help you troubleshoot all three of the above. With this basic info under our belts, let's turn the page and get testing!.....