START HERE: Troubleshooting DTC P0122
What's gonna' help us diagnose and repair the P0122 TP Sensor Circuit Low Voltage OBD II diagnostic trouble code (DTC), that's lighting up your check engine light, is remembering/knowing that the throttle position sensor (TPS) is stuck producing a low voltage.
I can illustrate this a bit better by saying that the PCM ‘thinks’ the throttle plate is closed (like when the engine is idling at a stop light and/or your foot is off the accelerator pedal) the whole time the engine is running while you're driving around town.
By testing the TP sensor with a multimeter (while it's still on the throttle body and connected to its electrical connector), you and I can find out if it's truly fried or not.
Here's a brief description of the tests you'll be doing with the help of this tutorial:
- Check the TP sensor's signal with a multimeter.
- You'll be connecting your multimeter to the TP sensor connector's middle wire and then manually opening and closing the throttle to see if the TP sensor produces a varying DC voltage signal.
- TEST 1: Testing The TPS Signal.
- Verify that the TP sensor is getting power (if TEST 1 is failed).
- This is a simple multimeter test too.
- TEST 2: Verifying The TPS Has Power.
- Verify that the TP sensor is getting Ground (if TEST 1 is failed).
- This is a simple multimeter test too.
- TEST 3: Verifying The TPS Has Ground.
TPS TEST 1: Testing The TPS Signal
The first order of business, is to test the throttle position signal right off the bat. Depending on your TPS test result, you'll be able to condemn the TPS as bad or continue on to the next tests.
I've divided the test into three parts. To accomplish the steps in PART 3, you'll need a helper.
NOTE: To ensure the accuracy of your test, it's best to test the throttle position sensor (TPS) with the engine warmed up.
OK, let's start:
Select Volts DC mode on your multimeter and with the red multimeter test lead probe the wire labeled with the number 2 in the photos. This is the circuit that supplies the TP Signal to the PCM.
If you don't have a multimeter or need to upgrade yours, check out my recommendation: Buying A Digital Multimeter For Automotive Diagnostic Testing (found at: easyautodiagnostics.com).
NOTE: The throttle position sensor, must be connected to its electrical connector during this test (this is where a wire piercing probe comes in handy. To see what one looks like, click here: Wire Piercing Probe Tool).
Ground the black multimeter test lead on the battery negative (-) terminal. Have your helper turn the key to the ON position, but don't start the engine (this will power up the TP sensor).
With the Key On Engine Off (KOEO), you should see 0.5 to 0.9 Volts DC on your multimeter. If you don't, don't worry about it just yet, continue with the other steps.
Now, slowly open the throttle (by hand and from the engine compartment) while you observe the change in voltage numbers on your multimeter.
For this test result to be accurate, you need to open the throttle by hand and not from inside the vehicle.
As the throttle opens, the voltage numbers will increase. This increase in voltage should be smooth and without any gaps or skips. Once the throttle is wide open, your multimeter should read somewhere between 3.5 to 4.9 Volts DC.
Now, slowly close the throttle. As the throttle is closing, you should see the voltage decrease smoothly and without any gaps or skips, to the exact same voltage you noticed in step 4.
OK, now you'll need someone to help you lightly tap on the throttle position sensor with the handle of a screw-driver (or something similar, and I want to emphasize the words ‘lightly tap’) as you slowly open and close the throttle and observe the multimeter.
If the TPS is bad, the tapping will cause the voltage numbers to skip or go blank. If the TPS is OK, the tapping will have no effect on the voltage numbers.
Repeat step 7 several times to make sure of your multimeter test results.
Let's take a look at your test results:
CASE 1: The multimeter registered a smooth increase or decrease in voltage with no gaps. This tells you that the throttle position sensor itself is OK and not causing the issue you're trying to troubleshoot.
This test result also let's you know that the problem causing the P0122 trouble code is intermittent and not present at this point in time.
CASE 2: The multimeter DID NOT register a smooth increase or decrease in voltage, and you saw the voltage reading skip or go dead when tapping the TPS. This means that the throttle position sensor (TPS) is bad. Replace the throttle position sensor.
CASE 3: The multimeter DID NOT register any voltage. This test result doesn't condemn the TPS as bad just yet. Why?
Because the TPS may be missing either power or Ground. So the next step is to check that the TPS is getting power, go to: TPS TEST 2: Verifying The TPS Has Power.