TEST 2: Verifying Throttle Position Sensor Has Power
So far you have confirmed that the TPS is not producing an increasing/decreasing throttle position voltage signal. The next step is to make sure that it's getting power (5 Volts DC).
The wire that feeds this power is the brown with white stripe (BRN/WHT) wire of the TPS engine wiring harness connector.
To check for these 5 Volts all we need to do is a very simple multimeter voltage test. So, without further ado, let's get testing:
Place your multimeter's dial in 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 BRN/WHT wire of the TPS connector with the red multimeter test lead. The BRN/WHT wire is the one that connects to TPS pin #1 in the illustration above.
IMPORTANT Use a back probe or a wire piercing probe instead of probing the front of the connector. Probing the front of the connector will damage it.
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:
Let's take a look at your test results:
CASE 1: The BRN/WHT wire has 4.5 to 5 Volts. This means that the throttle position sensor (TPS) is getting power from your 2.0L Ford Escort ZX2's fuel injection computer.
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: The BRN/WHT wire DOES NOT have 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 this test result tells you that the TPS itself is not at fault (and thus causing the TPS trouble code). Without power, the TPS can't create a throttle angle voltage signal. 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, we're gonna check that the gray with red stripe (GRY/RED) wire of the TPS engine wiring harness connector is feeding the TPS with ground.
Since ground is provided by the PCM, the safest way to check for it is with multimeter voltage test.
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.
Check the GRY/RED wire of the TPS connector with the red multimeter test lead. The GRY/RED wire is the one that connects to TPS pin #3 in the illustration above.
IMPORTANT Use a back probe or a wire piercing probe instead of probing the front of the connector with the multimeter probe.
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.
Let's find out what your test result means:
CASE 1: The multimeter registered 10 to 12 Volts, confirming the GRY/RED is feeding Ground to the TPS. This is the correct and expected test result and confirms the TPS is getting Ground.
Taking into account the test results of all 3 test, you have confirmed that:
- The TP sensor is not providing a varying voltage signal when manually opening 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).
Therefore, 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: The multimeter DID NOT register 10 to 12 Volts, confirming the GRY/RED IS NOT feeding Ground to the TPS. 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 2.0L Ford Escort ZX2 as being the cause of the problem and/or the TP sensor diagnostic trouble code (DTC) lighting up the check engine light (CEL).