TPS TEST 2: Verifying TPS Has Power
Terminal number 3, of the TP sensor's harness connector, is the one that feeds the sensor with 5 Volts DC.
If these 5 Volts are missing then the throttle position sensor won't create a throttle angle signal.
So, in this test we'll do a simple voltage test with the multimeter to check for them.
NOTE: You can test for these 5 Volts DC with the TP sensor connected or disconnected to the TPS. I personally prefer to do this test with the TP sensor's connector unplugged.
This is what you'll need to do:
Place your multimeter's dial in Volts DC mode.
Probe the number 3 wire, with the red multimeter test lead and an appropriate tool (like a Wire-Piercing Probe). The throttle position sensor's connector can be connected to the sensor or not when you probe this circuit.
IMPORTANT: If you probe the front of the TPS harness connector, be careful and don't damage the terminal. Damaging the terminal will require that you replace 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: The multimeter registered 4.5 to 5 Volts. This tells you that your 4.0L Jeep's TPS is getting power.
The next step (and the last test) is to check that terminal number 1 of the TP sensor's harness connector is providing Ground. For this test, go to: TPS TEST 3: Verifying TPS Has Ground.
CASE 2: Multimeter DID NOT register 4.5 to 5 Volts. Double check all of your connections and repeat the test. If your multimeter still doesn't register the 4.5 to 5 Volts DC...
, then you've just eliminated the TP sensor itself, on your Jeep, as bad. The two most likely reasons for this are: 1) an open in the wire between the TP sensor's harness connector and the PCM's harness connector or 2) the PCM may be fried (although a bad PCM is very rare).
Although it's beyond the scope of this article to test these two conditions, you have now eliminated the throttle position sensor (TPS) on your Jeep as being the cause of the problem and/or the TPS diagnostic trouble code (DTC) lighting up the check engine light (CEL).
TPS TEST 3: Verifying TPS Has Ground
Ground is fed to your 4.0L Jeep Grand Cherokee's (Cherokee, Wrangler) TP sensor by terminal number 1 of the sensor's harness connector.
So, in this last test, we'll check this Ground by doing a simple voltage test with the multimeter.
IMPORTANT: Be careful and don't accidentally or intentionally apply power (12 Volts) to this circuit or you'll fry the PCM since it's the PCM that provides this Ground internally.
OK, here are the test steps:
With your multimeter still in Volts DC mode from TPS TEST 2.
Probe the wire labeled with the number 1 in the photos with the black multimeter test lead. The TPS connector can be connected or not to the Sensor.
It's important that you do not probe the front of the connector or you run the risk of damaging the terminal.
Now, with the red multimeter test lead, probe the battery positive (+) terminal.
Once again, when everything is ready, have your helper turn the Key to its ON position but don't start the engine.
If this circuit is OK and the PCM is providing a good path to Ground, your multimeter will display 11 to 12 Volts.
Let's take a look at your test results:
CASE 1: The multimeter showed 11 to 12 Volts. This confirms that the PCM and the wire/circuit (that supply this Ground) are OK.
All three test have confirmed that:
- The TPS is not providing a varying voltage signal when manually opening the throttle plate.
- The TPS is being fed 5 Volts DC.
- The TPS is being fed ground.
Therefore, you can conclude that the TP 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 multimeter still doesn't show the indicated voltage...
...then this indicates a problem with either your Jeep's PCM (internal fault/problem) or an open in the wire between the TPS harness connector and the PCM's harness connector
Although testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your Jeep as being the cause of the problem and/or the TPS Diagnostic Trouble Code (DTC) lighting up the check engine light (CEL).