2004 Ford Focus ZX5 2.0L intermittent stalls no communication

Car Question:

My car would stall intermittently and has no communication with generic scanner (the ones you buy online or local parts store). It is too expensive to have this diagnosed by a garage, can I do this myself? What tools do I need?

ATS Adviser:

You can fix this type of problem by using any generic scanner with live data stream along with a decent voltmeter with MINMAX features. Start testing by going to pin 4 and 5 at DLC (where you plugin the scanner). These pins are ground terminals and should read no higher than 0.250 volt at key on engine off (KOEO). Then measure pin 16 (power supply) and should be battery voltage.

This car carries Ford high speed CAN data network thru pin 6 and 14. At KOEO with pin 5 as ground, both high speed pins should average 2.5 volt by setting up the voltmeter at MINMAX. Low speed data bus signals are carried by pins 13, 10, 7 and 2 at DLC. Low speed bus voltage should read 7 volts at KOEO.

Using the PCM as the hub module for the bus network system, testing for no communication is done by unhooking all the other modules based on network speed. To test high speed bus network network use pin 6 and 14 to test the instrument cluster, the only high speed module besides the PCM. For testing low speed modules, use pins 13, 10, 7 and 2 of the DLC terminals. A detailed volt and ohmmeter readings can be seen in details if you get hold of the engine computer data lines diagram.

Final Fix:

Fixed! Monitoring the scanner while disconnecting each of low speed modules, found GEM module was defective. A new one from the dealer fixed the problem. Thanks!

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