TEST 2: Verifying Throttle Position Sensor Has Power
If you've reached this point, your multimeter has confirmed that the TPS is not creating an increasing/decreasing throttle position (TP) voltage signal. In some rare cases, this is due to the fact that the TPS is either missing power or Ground. So, in this test step we're gonna' make sure it's getting power.
The throttle position sensor connector's wire that feeds this power (5 Volts DC) to the TPS is the orange (ORG) wire. This ORG wire connects to TPS terminal #1 in the illustration above.
These are the test steps:
Set your multimeter to Volts DC mode and turn the key on but don't start the engine.
This will power up the TP sensor's connector.
Check the TPS connector's ORG wire with the red multimeter test lead (see the illustration above).
IMPORTANT Avoid probing the front of the TPS connector. Probing the metal terminal of the TPS connector, with your multimeter's test lead, could damage it and require that you replace the connector. Use a back probe or a wire piercing probe instead of probing the front of the connector.
Connect the black multimeter test lead to a good and clean Ground point on the engine or directly on the negative (-) battery terminal.
When you've set up the test, have a helper turn the Key On Engine Off (KOEO).
Your multimeter should display 4.5 to 5 Volts on its screen. OK, now let's interpret your test results below:
CASE 1: Your multimeter confirms that the ORG wire has 4.5 to 5 Volts. This tells you that the TPS connector is feeding the TPS with power.
The next and last test, is to make sure that the throttle position sensor is getting Ground (from the PCM too). For this test, go to: TEST 3: Verifying Throttle Position Sensor Has Ground.
CASE 2: Your multimeter confirms that the ORG wire DOES NOT have 4.5 to 5 Volts. Double check that you're testing the ORG wire and repeat the test. If your multimeter still doesn't show the 4.5 to 5 Volts DC...
.. then this test result tells you that the reason the TPS is not creating a proper TP voltage signal (in TEST 1) is due to a lack of power. Since the PCM provides this power, the most likely culprit is an open in the ORG wire between the TPS connector and the PCM connector. Although beyond the scope of this tutorial, your next step is to diagnose and restore this missing power.
TEST 3: Verifying Throttle Position Sensor Has Ground
In this last test, you're gonna' make sure that the TPS is being fed ground. Ground is fed by the black with light blue stripe (BLK/LT BLU) wire. The BLK/LT BLU wire is the one that connects to TPS pin #3.
To check for the availability of ground, you'll do a simple voltage test with your multimeter very much like the one you did in TEST 2.
IMPORTANT: Ground is provided directly by the fuel injection computer. Be careful and don't intentionally or accidentally short this wire (circuit) to battery power or you will fry the fuel injection computer.
OK, here are the test steps:
Set your multimeter to Volts DC mode.
Probe the TPS connector's BLK/LT BLU wire with the black multimeter test lead.
Avoid probing the front of the TPS connector. Probing the metal terminal of the TPS connector with the multimeter test lead could damage it (and require that you replace the connector). Use a back probe or a wire piercing probe instead of probing the front of the connector.
Now, with the red multimeter test lead, probe the battery positive (+) terminal.
Turn the Key to its ON position but don't start the engine. This will power up the fuel injection computer.
Your multimeter will display 11 to 12 Volts if terminal B is feeding the TPS with ground.
CASE 1: The multimeter showed 11 to 12 Volts. This is the correct and expected test result and confirms the TPS is getting Ground.
You can conclude that the TPS is bad only if you have confirmed that:
- The TP sensor is not creating an increasing/decreasing voltage signal when manually opening/closing the throttle plate (TEST 1).
- The TP sensor is being fed 5 Volts DC (TEST 2).
- The TP sensor is being fed Ground (TEST 3).
Taking the 3 test results above, you can conclude that the throttle position sensor is bad and needs to be replaced (and that this will solve the TP sensor code lighting up the check engine light).
CASE 2: Multimeter DID NOT show 11 to 12 Volts. Double check that you're testing the correct TP sensor harness terminal wire and repeat the test.
If your test result still indicates that the TPS is not getting ground, then we can conclude that one of two things are causing this lack of ground:
- There's an open in the wire between the TP sensor harness connector and the fuel injection computer's harness connector.
- The fuel injection computer has an internal problem (although this is extremely rare).
Although testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your 4.7L Jeep as being the cause of the problem and/or the TP sensor diagnostic trouble code (DTC) lighting up the check engine light (CEL).