Ground points under the MAP sensor

[petervankleeck]

Gentlemen, what do you suggest is the best way to access the ground points attached under MAP sensor? My car has been running great but the SYS warning flashes intermittently throwing the C41 code. Sometimes it clears up right away (flashes once or twice) and goes away. Sometimes it flashes once when I start the car. Sometimes it flashes until I get home and clears up after I start the car again. I'm going to check all the grounds. BTW, the new Registry shirts are really nice.

Any help will be greatly appreciated.

Thanks!

Peter

[Hib Halverson]

Map sensor grounding may or may not be the problem.

CCM code C41 sets when the ECM serial data is not detected by the CCM.

My suggestion first would be to take a look at FSM pages in Section 8 on CCM diagnostics under "ECM Serial Data Circuit" (loss of communications).

[Paul Workman]

Originally Posted by petervankleeck

Gentlemen, what do you suggest is the best way to access the ground points attached under MAP sensor? My car has been running great but the SYS warning flashes intermittently throwing the C41 code. Sometimes it clears up right away (flashes once or twice) and goes away. Sometimes it flashes once when I start the car. Sometimes it flashes until I get home and clears up after I start the car again. I'm going to check all the grounds. BTW, the new Registry shirts are really nice.

Any help will be greatly appreciated.

Thanks!

Peter

Well, it does sound like a connection issue - either the serial data link or too, grounding can't be ruled out either.

To answer your question RE grounding points under the MAP sensor, there are two major grounding terminals to which many circuits, including the CCM are connected. And, b/c so many circuits are tied to those two points, if you have never serviced them it wouldn't be wrong to do so - might not be your problem but you can "kill many birds with (a couple) stones - including issues you have yet to experience - by doing so. But, as Hib suggests, follow the FSM diagnostics tree first: it may eventually lead to grounding anyway.

From memory (uh-oh...) you will need to remove the MAP sensor bracket (the sensor will come with it) and the fuel tree to access the two ground points.

I suggest you tie-wrap the wires leading to their respective ground points before removing the bolt securing the individual lugs. (Otherwise, they will retract every which way and you will play hell trying to round them up again...ask me how I know!)

Aluminum oxide film is nearly impossible to see with the naked eye, so even if the lugs look like bare metal, you should brush each lug - both sides - with a wire brush or with Scotch Brite or emery cloth and wash them with Electronic Cleaner (ideal) or brake cleaner. And, for good, long lasting (i.e., years!) of trouble free service, a thin coating of dialectic grease on each lug before installing the hold-down bolt and a new star washer.

For tools, I have a Craftsman 1/4" drive ratchet and metric sockets that worked well, I found. Just don't drop the ratchet (between the bell housing and the trans tunnel. ! I did that once and try as I might, I NEVER could find the SOB again!!

[petervankleeck]

Paul, thank you for your very helpful post. I just cleaned up the negative battery cable ground to the frame and so far no codes. I'm also going to get into the ground bundles as you suggested.

Thank you for your expertise and willingness to assist with ZR1 and LT5 questions.

Peter, 1990, #659