I own a vehicle that has given me a lot of grief recently due to short circuits.
The benefit of this is that I have undertaken a class on professional automotive electronics diagnostics and repair and so I would say I am fairly good at fixing vehicular electrical/electronic faults, except of course this one that I am talking about.
The manufacturer provides two methods of identifying short circuits:
a. for circuits not connected to a control unit b. for circuits connected to a control unit
The circuit I am trying to troubleshoot is connected to a control unit.
The first set of instructions read as follows:
- remove the fuse and main fuse of the circuit
- disconnect all connectors of electrical components in the circuit
- attach a voltmeter to the fuse box and reconnect each connector beginning nearest to the power source
- check the voltmeter reading as the connections are reconnected
A short has occurred where the voltmeter reading changes
This will help to confirm or deny if there is a short that has resulted in/from a fuse melting, or a solenoid operating when the ignition switch is one or a CPU transistor burns out when the ignition switch is turned on.
This is why I am stupefied!
According to the wiring diagram for the problem circuit, there are several fuses! There is an engine fuse of 30A in the engine compartment which I think should qualify as the main fuse, and there are three more fuses in the left kick panel inside the vehicle, another engine fuse rated at 10A and two more meter fuses one rated at 15A and another rated at 10A.
My first question is - to which of these fuse connectors should I be taking the voltmeter reading at?
There second set of instructions for finding a short follows immediately below and it involves three steps:
- Attach the voltmeter to the CPU connector
- Connect to the Switch/sensor connector
- Check the voltmeter reading
A short has occurred where the voltmeter reading is 0V
This will help to confirm or deny if there is a short that has resulted in/from the CPU thinking the switch is on because the same conditions exist as when the switch is on; as well as where the CPU sensing the sensor to be 0 Ohms because the same conditions exist as when the resistance value is 0 Ohms; or the CPU equipped with the self-diagnosis function outputs the code.
My second question is how exactly am I supposed to attach the voltmeter to the CPU connector?
I have attached a copy of the picture that came along with this instructions in case I can get some help to gain some clarity on what exactly I need to do!
NOTE: I will edited the part of the instructions that talk about using a test light because I prefer to use a multimeter!
Schematics of the circuit has 3 parts,
The voltage drop readings should be as follows ( manufacturer specifications)
IMRC TERMINAL 1 at idle = B+
IMRC TERMINAL 1 at 3,300RPM = Below 1.0V
IMRC TERMINAL 2 at Ignition ON = B+
IMRC TERMINAL 2 at Ignition OFF= Below 1.0V
IMRC TERMINAL 3 at all times = Below 1.0V
IMRC TERMINAL 5 at idle = 5V
IMRC TERMINAL 5 at 3,300RPM = Below 1.0V
IMRC TERMINAL 6 at all times = Below 1.0V
The voltage drop readings in my vehicle are as follows
IMRC TERMINAL 1 at idle = Below 1.0V (about 0.04V to 0.08V)
IMRC TERMINAL 1 at 3,300RPM = Below 1.0V (about 0.04V to 0.08V)
IMRC TERMINAL 2 at Ignition ON = B+
IMRC TERMINAL 2 at Ignition OFF= Below 1.0V (about 0.10V to 0.11V)
IMRC TERMINAL 3 at all times = Below 1.0V (about 0.03V to 0.04V)
IMRC TERMINAL 5 at idle = 5V
IMRC TERMINAL 5 at 3,300RPM = 5V
IMRC TERMINAL 6 at all times = Below 1.0V (about 0.05V to 0.08V)
These are the full diagrams for testing for short circuits in both circuits connected to a control unit and circuits without a control unit
POSTSCRIPT:
One of the reasons why I came here was persistent short circuits between IMRC Terminal 2 and body ground; IMRC Terminal 5 and body ground; IMRC Terminal 5 and power supply and finally IMRC Terminal 6 and power supply.
I finally fixed all these short circuits - it was from one of the oxygen sensors.
This leaves me with a faulty ECU. This diagram explains how the entire circuit works, it looks like. The problem appears to be between IMRC Terminal 1 and PCM Pin 42, which is now permanently closed.