I saw 3 or 4 Mach RCU's at Pull-a-part just last week when I was down there scavenging. They charge $18 for them.
I have a spare one right now that I've been using for testing, but if you're really in need I could part with it and just pick up another next time I'm in the junkyard?
Let's do diagnostics on the radio first.
Turn the system on, and have it in AM or FM mode. Hold down buttons 3 and 6 simultaneously for a few seconds. The ICP
will stop whatever it was doing and show "SP" on the display, and now it's in self-diagnostic mode.
Press button 1 now, and it will run a self-test, and flash SELF while it's doing it. When it stops flashing, you can hit the "tune up" button to show any error codes. It only has six:
0 No DTCs logged
1 No response from RCU
2 No response from cassette player
4 No response from CD player
7 No response from remote climate control
9 ROM Verification failed (memory/circuit related error)
Buttons 2 and 3 read off feature or product variant codes, not really relevant here.
Button 4 however, is the RCU
self-test. Unfortunately it's not exactly all that great a test, it just verifies functionality of some of the ROM and EEPROM chips inside it. It's something though. After hitting button 4, you should get another code on the panel telling you what the RCU
found. Code "F" means everything passed. I've attached a chart with the codes.
Button 5 then tests the ICP
display panel itself. (probably useless)
If everything passes, it still sounds like it's the RCU
, but I'd get our the multi-meter and test some of the important wires to be sure, as it would be really annoying to drop in a new RCU
and still get no sound due to a cut circuit somewhere or something.
The most relevant I think should be:
At the ICP
- pin 4 (green w/ black stripe) - should have voltage (12V+) when system is on (this is factory remote turn-on equivalent)
At the RCU
- lefthand harness ("a") - pin 14 thick gauge yellow wire - should be 12V+ at all times.
- middle harness ("b") - pin 17 red w/orange stripe - should be 12V+ in start, park, and neutral.
- pin 2 - other end of audio-system-on again, green w/ blk stripe
- pins 1 & 15 (blue w/pink & tan) - check that there's about 4v between these two. This is the CAN ACP bus from the ICP
. If this bus is disrupted, the RCU
would never get the commands from the ICP
to change channels, turn vol up, etc. Tan wire is negative.
Here's a pinout of all the harnesses with more description in case you want to test other circuits: https://drive.google.com/open?id=11q...LskQ6H_bdnoi8Y
The colors are sometimes slightly different in some years I've found, put the pin locations seem to stay consistent.
Edit: typoed a number.