I have a 1996 Ford Explorer Sport 4.0L. The other day I tried to get a inspection and the inspector said the computer failed to communicate. So went home with the car and checked the obd2 connector for power. According to my wiring diagram
Pin 2-data bus(+) to ecu- pin 15 or 16?
pin4 & 5-Ground -to G100 and G101 one near radiator left side and other on left side on top half way down fender
pin 7-Power Ground? Seems to go to abs,airbag,locks etc
Pin10-Data Bus (-)- to ecu pin 15 or 16?
Pin13-Programming signal -To ecu pin 13
Pin16-Constant + from inner fuse panel.

I checked for power pin 16 by using a multimeter by ground the neg pole and checking 16 with positive pole. I had battery voltage.

Then checking ground pins 4 and 5 by putting + pole on pin 16 and probing 4 and 5 with negative pole. They both had battery voltage.

I did a resistance test on pin 2,10,13 from OBD2 connector to ecu and they were all under .5 ohms.

I also resistance tested pin 7 to the all the units the light blue/white and they were fine.

When i put in my small scanner (Mac scanner was a cheap $60 unit) it lights up and when i go to connect the message stops at ISO when its connecting.

Is there any information on how to really test the obd2 pins, i can't understand why the scanner will not connect it always worked before and I did try my friends scanner and it had the same problem. I have access to a oscilloscope but once again no information.

Did a pin test got these results

Pin 2 0V ign off and 0V ignition on
Pin 4 .1 ohm
pin 5 3.0 ohms*too much?
pin 7 5V Ignition off 8.95V ignition on
pin10 0V ignition off 5V ignition on
Pin 13 0V ignition off 0V ignition on
Pin 16 Battery voltage either way


Any ideas?

 

Can you try this ?
Disconnect the following sensors and see if the scan tool will start communicating.
The DPFE and crankshaft sensors. If still no communication disconnect a bunch of sensors until the scan tool can communicate. Then start reconnecting them one at a time and when the communication is cut off that is the shorted sensor.
Once you can get communication see if you can get any U codes like U1262 for an SCP network fault.

 

Disconnected the tps,iac,map,crankshaft sensor,etc the check engine is not lit but no communication. I just ordered a ecu, Pin2,4,5,10,16 are all working properly and from the manual i found that's all i would need to communicate can't see anything else that it could be, odd how car runs and the check engine comes on but no communication.

 

There are several areas that must clear for communication to take place. A PCM,ECU is a possibility, but we like to eliminate the other lower cost items first. One of the main reasons for loss of communication is a short circuit in the system and a sensor is one of the possibilities . The DPFE is one of the common ones. The GEM module which controls a lot of functions is also a possibility. Let us know if the ECU replacement takes care of the problem.

 

That DPFE sensor was one i unplugged actually. Any tests I should consider while i wait for ecu?
How would i test the GEM from what i saw it was tucked into the dashboard? Also how would I test the DPFE?
Why would those affect communication between scan tool? PCM checks these sensors before hand?

I saw on the diagram Pin 7 was linked to all the auxiliary modules such as the GEM ,antilock,airbag,locks,etc. Wouldn't those be on a separate circuit even though they have certain inputs that go to the pcm?

Also is it true the scan tool could connect without pin 7 or is that some type of myth?

 

Also I just found a post "OBD2 Connection Need Help" where a crown vic had basically the same problem

"OBD2 Connection Need Help
1997 Crown Vic. Several different scanner tools and the computer at the inspection station can not connect to the PCM. EEC-V DLC pin out is:
Pin 2, 0 VDC, Pin 4 is 1.0 ohms to gnd, pin 5 is 0.6 ohms to gnd, pin 7 is 12 VDC, pin 10 is 5 VDC, pin 13 is 0.53 VDC, and pin 16 is 12 VDC.
All grounds at 104 pin PCM connector are good.
Any ideas?"

He ended up replacing the ECU

only difference I have is the 12 Volts on pin 7.

Would there be an issue there once again with pin 7 being a barrier to Connect?

 

Pin 7 is the ISO 9141 and 9141-2 line normal 12 volts. That line is used strictly for scan tool communication.
It does look like there could be a PCM (ECU) problem. Do you have any aftermarket additions on the vehicle?

 

No aftermarket parts radio especially. The pin 7 is dedicated for scantool communication? But would that just be for the rest of the modules?
The car runs with all auxiliary modules unplugged minus the GEM i couldn't get to.
The the low volts in pin 7 wouldn't that be a problem with an auxiliary module and not the pcm or does the voltage for them come from PCM?

 

It doesn't make that much difference in how the vehicle runs, it's a communication problem. Did you disconnect the air bag module in your checking procedure?

In your wiring diagram, where does pin 7 get it's voltage? In the original post you posted, you listed the abs, door locks,air bag etc., did you disconnect those modules from the system? If not, that's what you need to do .

 

Pin 7 is ISO link/diagnostic input for the GEM.

Shared splice,,

Air Bag Diagnostic monitor
Remote Anti Theft Module, RAP
4WABS Control
Auto ride Control module, ARC