PCM won't respond to emissions test device

Your PCM relies on two fuses and one diode. Go to the fuse block in the passenger compartment, passenger side kick panel near the right floor. Look for fuse #7 rated 5 amps. Now go to the engine compartment, power distribution box, look for fuse #18 rated 40 amps. Also in that box is a "Diode". Check that too. I used to test diodes with voltmeter. With voltmeter on "ohms" setting. There should be continuity one way but not the other. Try different settings if it doesn't respond. Be sure to plug "diode" back in the same position (polarity) as it came out. Don't reverse it. Good Luck.

Very helpful! However, I have a 2005 Lincoln LS and #18 on the panel requires a 20 amp - (yellow color) instead of a 40 amps. Additionally, those two were okay, but he replaced #6 (10 amps - red color); unfortunately with the 20 amp fuse (got to get someone to replace it. Such a difficult place to access the fuse panel! According to the manual, the 2005 LS fuse rating max out at 20 amp. It's connected, but it did not pass due to P0128 - Coolant Thermostat and P0420 - Catalyst System Efficiency Below Threshold (Bank 1). Hope this information helps someone else!