If you've been wanting to know how to check the continuity of the wires between the throttle position sensor (TPS) and the PCM... well then, this is the tutorial you've been looking for.
This tutorial will help you find out if there's an ‘open’ in the wiring between the throttle position sensor and the PCM (which could lead to a continuous TPS trouble code that won't go away).
Before testing the continuity of the TPS circuits (wires), you need to first make sure that the TPS itself is OK. The TPS can be tested with a simple multimeter and you find the test explained in a step-by-step manner here: How to Test the 4.6L, 5.4L Ford Throttle Position Sensor (TPS) (at: easyautodiagnostics.com).
The contents of this tutorial at a glance:
- Important Safety Precautions.
- What Tools Do I Need to Test the TPS Wires?
- TEST 1: Check the Basics First.
- TEST 2: Checking Continuity of the TP Signal Circuit.
- TEST 3: Checking Continuity of the 5 V Reference Circuit.
- TEST 4: Checking Continuity of the Ground Circuit.
- TEST 5: Checking TP Signal Circuit For Short to Power.
- TPS Power and Ground Circuits Shorted to Power or Ground.
- More Ford 4.6L, 5.4L Diagnostic Tutorials.
Important Safety Precautions
TIP 1: Never probe the front of the PCM 104 pin connector.
Probing the front of the 104 pin PCM connector can/will damage the round metal terminals (of the connector). If this happens... you're looking into a MAJOR nightmare since you'll have to replace the entire engine wiring harness.
TIP 2: The battery negative terminal needs to be disconnected before you unplug the PCM from its 104 pin connector.
This is important for two specific reasons: One, it'll avoid damaging the PCM due to a voltage spike. Two: It'll avoid damaging your multimeter by making sure the circuit you're testing doesn't have power.
TIP 3: Use the recomended tools to test the continuity between the PCM and the TPS.
If you don't have the tools (or can't afford to buy them), then I suggest taking your vehicle to a professional repair shop that does have them.
Don't let the fact that you don't have the appropriate tools discourage you. My suggestion is to take a look at the tutorial and familiarize yourself with the test procedures. This will help you comunicate the issue (and what you want done) more effectively if you decide to take your Ford vehicle to a repair shop.
Before we start testing... you need to know that a special tool is needed to test the continuity of the wires between the throttle position sensor and the PCM 104 pin connector (it'll also let us check the live signals coming from and going to the PCM).
This tool is a breakout box. What does it do? It allows us to safely check the circuits that connect to the PCM without having to hack into the wires of the PCM connector.
As you can see in the photo in the image viewer... this tool resembles a ‘box’ that has two connectors. One connector connects to your Ford's PCM. The other connector connects to the PCM's engine wiring harness PCM connector. The ‘box’ part of the tool has 104 slots that can be probed with a multimeter test lead.
The breakout box is designed to help us avoid:
- Back probing (with a back-probe) the back of the PCM connector to test a specific circuit.
- Probing the front of the PCM connector (something that should NEVER be done since this will damage the terminal being probed).
- Using a wire-piercing probe on the wire of the PCM connector that's being tested.
Currently, there are two flavors of this breakout box: The OTC-3235 Ford EEC-V 104 Pin Breakout Box and the Ford Rotunda 014-00950
You may also be wondering if you can test the wires between the TPS and the PCM without a breakout box... and the answer is yes. Because of the risk of damage to the PCM 104 pin connector and the availability of the breakout box for the Ford vehicles covered by this tutorial... this tutorial focuses on the use of the breakout box.
Here's a list of other tools you'll need (besides the 104 pin breakout box):
- Wiring diagram.
- PCM 104 pin connector pin-out chart.
TEST 1: Check the Basics First
I'm sure you're itching to get started and get testing to see if the one of the 3 wires of the throttle position sensor's connector has an open or a short...
... But to succesfully diagnose these conditions, you need to have done a few things before.
Don't worry, most of the basic pre-checks are just checking for obvious damage or problems.
Here's the list of the things you should already have checked/confirmed:
- The throttle position sensor (TPS) itself is not defective. Either because you replaced it with a new one or you have tested it.
- The throttle cable, that connects the accelerator pedal to the throttle plate, is not binding, broken, or damaged in any way and causing the throttle plate to not fully close or move in a smooth way.
- The throttle plate opens and closes without binding.
- The idle stop screw adjustment (on the throttle body) has not been altered in any way.
- This usually happens when the engine is ‘idled up’ so that the engine will rev at a higher RPM (at idle) to mask such problems as a rough idle condition.
- The BRN/WHT wire of the TPS connector does (or does not) have 5 Volts DC with the Key On Engine Off (KOEO).
- The GRY/RED wire of the TPS connector is (or is not) feeding ground.
Making sure that the above are OK or that a problem exists (that needs to be remedied) will help you save a ton of frustration, time and money.
To check that the BRN/WHT is (or isn't) providing 5 Volts DC and the GRY/RED wire is (or isn't) providing ground, see this tutorial:
- How to Test the 4.6L, 5.4L Ford Throttle Position Sensor (TPS) (at: easyautodiagnostics.com).
The following article has a simplified wiring-diagram that may also be of help:
OK, if all of the above check out OK, then your next step is to make check the continuity of the throttle position sensor's wires between the PCM connector and the TPS connector.