TEST 2: Verifying Throttle Position Sensor Has Power
If in TEST 1 the throttle position sensor DID NOT report an increasing/decreasing throttle angle voltage as you opened/closed the throttle plate, then we need to make sure that the TPS is being fed power and Ground before concluding the sensor has failed.
In this test step, we're gonna' make sure that the TPS is being fed power. This power is in the form of 5 Volts and are provided by your Corolla's fuel injection computer.
The wire that feeds this voltage to the TPS is the one that connects to terminal 4 of the TPS engine wiring harness connector (as identified in the illustration above).
OK, to get this test under way, these are the test steps:
Place your multimeter's dial in Volts DC mode.
Turn the key on but don't start the engine.
This will power up the TP sensor's connector.
Probe the TPS connector terminal that corresponds to pin #4, of the TPS connector, with the red multimeter test lead.
IMPORTANT Be careful when probing the metal terminal of the TPS connector. Damaging the terminal will 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:
Let's take a look at what your test results mean:
CASE 1: Your multimeter registered 4.5 to 5 Volts. So far so good since this tells you that the throttle position sensor (TPS) is getting power from the powertrain control module (PCM).
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 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 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 step, we're gonna' make sure that the throttle position sensor is being supplied with a good Ground.
This Ground is supplied by your Corolla's fuel injection computer. The wire that feeds the TPS with this Ground is the one that connects to terminal number 1 of the TPS engine wiring harness connector (see illustration above).
IMPORTANT: Be careful and do not accidentally or intentionally short this Ground circuit to battery voltage or you'll fry your Corolla's fuel injection computer.
These are the test steps:
Set your multimeter to Volts DC mode.
Probe the TPS connector wire that connects to the TP sensor's pin #1 with the black multimeter test lead.
Be careful not to damage the terminal if you probe it on the front of the connector. If possible, you should use a back probe or a wire-piercing probe to check this circuit.
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 PCM.
Your multimeter will display 10 to 12 Volts if the BLK wire is feeding the TPS with Ground.
Let's interpret your test results:
CASE 1: The multimeter showed 10 to 12 Volts. This tells you that the throttle position sensor, on your Toyota, is being fed with Ground from the PCM.
All three test have confirmed that:
- The TP sensor is not providing a varying voltage signal when manually opening the throttle plate.
- The TP sensor is being fed 5 Volts DC.
- The TP sensor is being fed Ground.
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).
After replacing the TPS you'll need to adjust it to the correct specification. To adjust the TPS, this tutorial's subheading ‘Adjusting The Throttle Position Sensor Assemby’ will help: TPS Idle Switch Multimeter Test (1.6L Toyota Corolla).
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 we can conclude that there's an open in the wire between the TP sensor harness connector and the PCM's harness connector. In the extreme of cases, the PCM has an internal problem (although this is very rare).
Although testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your 1.6L Toyota as being the cause of the problem and/or the TP sensor diagnostic trouble code (DTC) lighting up the check engine light (CEL).
If this info saved the day, buy me a beer!