Need to test your wiring? All cars use wiring harnesses to connect various
sensors and accessories to the computer ECU in order for the systems to work.
This guide will help when you have replaced a particular sensor such as a
camshaft angle sensor but still have the same trouble code.
What Goes Wrong?
The computer electrical system relies on a good connection between a sensor
or actuator and the computer. Over time engine vibration and road conditions such as heat,
rain, snow and the natural aging of wiring can cause these connections to become
loose, broken, damaged or corroded. This
causes the computer to think there is still a problem even though the component
has been replaced.
In this guide will be testing the camshaft angle actuator and position sensor
wiring because a code for the actuator
and sensor circuit is present and they both have already been replaced. The trouble code has been cleared and comes right
back after a few miles of driving. Let's jump right in.
Step 1: Locate and Disconnect Actuator Connector
Every sensor or actuator has a wiring connector. These connectors are
comprised of one or more terminals and can represent a computer ground, system
voltage and a reference and in some case an output wire that will control an
actuator or motor. Each sensor can use any number of terminals (wires) to
perform their task. The camshaft actuator below uses just two wires to do its
job. These two wires represent a power wire from the system and ground which is
controlled by the computer.
First we will check to see if the actuator is getting power. Disconnect the connector from the sensor. Check the wiring at the base of the
connector this is a popular place for the wiring to break. Look for broken or
loose wiring insulation or damaged pins as well.
Step 2: Check System Reference Voltage
Most sensors in a computer system run off of reference voltage, from 5 to 12
volts in most cases. This voltage is supplied by the computer or a fuse when the
system is turned on. The computer then uses this voltage to "power up" the
sensors, actuators or motors so it can make its readings and adjustments. This can also help see if
the computer system itself has power, you may have a simple problem such
as a blown
With the ignition key on,
voltmeter to DC voltage
. Then touch the negative lead to a good ground
source. Use the positive lead to probe the connector terminals you should be
able to find system voltage. System voltage is shared by most of the computers
sensors, actuators and motors.
Step 3: Check the Wiring to the Computer
For this step it helps to have a wiring diagram but it is not needed. All
computer wiring is identified by specific wiring color code such as, yellow and green yl/gn
which means yellow with a green stripe. The color motioned first is the
main color of the wire followed by the tracer color which will be a small line
on the wire.
This color code will be the same from the sensor to the computer. In this
example we will use the camshaft angle or position sensor. This is a three
wiring sensor, one wire is used for sensor power, the other two go directly into
the computer for sensing purposes. Once system power is confirmed with the key
on, the next step is to test the connection between the sensor and the computer
which will find broken wires.
Identify the connector wiring colors, you may need to strip the wiring cover
back to see the individual colors. These are the wires you will be looking for at the
computer ECU (engine control unit).
Locate the engine computer which is usually under the dash or in the engine
compartment. This one happens to be bolted to the air filter housing under the
Locate and release the wiring connector to gain access to the electrical pins
which connect the system wiring into the computer.
This will expose the connector pins which will be used for testing purposes.
While the connector is off check for the presents of engine oil which sounds
kind of weird but it has been known on high mileage engines that oil will seep
from the sensors, down the wiring and into the computer itself, like little
rivers of oil. If enough oil has been pushed into the computer it will short out
some of the internal components even though oil doesn't conduct electricity it
will saturate compounds which make up the chips, resistors, capacitors and
diodes. These connections must be clean and free from dirt, oil, rust and
The computer has many pins which connect to the various components. Once the
main connectors have been removed check the pins for rust or corrosion and clean
as necessary. It is a good idea to
spray electrical cleaner across these terminals and on the connectors.
You must gain access to the wiring at the computer to identify the incoming
wires. In this case we have removed the plastic cover over the connector. In
some cases the wires are exposed naturally.
All wires should be clearly visible, look around until you find the same wire
color combination and size present at the sensor.
Here is a wiring diagram that can help you see where the wire is headed in the
circuit and which pin number in the connector on the computer side. Again it
is not needed, but it's good to have for reference.
To make sure you are testing the correct wire count the places over in the
connector from one end or the other, in this case it is 8 places. This is so
when you turn the connector over you know which terminal to test from.
Now turn the connector over and count from the end that you referenced. This
will be the terminal used for testing.
Now take your
switch it to ohms. This will test the resistance in the wire if any. The
idea is to have none. Connect the probes to either end of the wiring connectors,
the meter with show the resistance in the connection. In this reading .6 is next
to nothing and acceptable so the wire is okay. When testing roll the test leads
in the terminal to ensure proper connection for a correct reading. If the ohms
reading are above 2.0 there is a problem with the wire and it needs replacement.
When testing try and wiggle the wires around while holding the test leads
steady this will simulate the engine vibrating which can help find intermitted
shorts, you might need a helper for this. While performing the test one of the
wires in the circuit was found to be bad and had to be replaced this fixed the
If you have any questions on how to test computer or sensor wiring
please ask our mechanics
are happy to help.
Article first published 2017-01-26