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Tuned Port Injection. A method of fuel injection, used on the early C4 Corvette L98 motor, (1985-1991). ...
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hcbph Random DTC41 Tip
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Thought I'd pass along a tip for anyone with a L98 engine that gets a DTC41 error code from an intermittent SES light.
Scenario is I started getting a SES light intermittently, it would come and go when driving or on startup. Typically if you disconnect the battery cable and hook it back up it would clear up the SES light. At no time did I have issues running the car but it didn't give me a warm and fuzzy when it happened. You won't always capture the error code but on occasion I would get the DTC41 error code.
I reviewed my notes on past issues on the car and had it happen 5 years ago (which I'd forgotten for the moment). I did the same fix and it seems to have solved it again. The fix is to disconnect all the ground contacts from the G104 ground on the engine block by the oil filter. Clean everything up, use dialectic grease on the connectors and put it back together. So far it looks to have taken care of it again.
The error code indicates a ECU failure, but the fact it's not continuous lead me to believe it was something else, a bad ground connection in this case.
The error code sucks as they don't describe the problem very well, hope this helps someone down the road.
Posted on: 6/25 3:17
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bogus Re: Random DTC41 Tip
Grand Imperial Pooh-Bah
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cool!!! Grounds are so important on plastic cars!!!
Posted on: 6/25 4:57
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Matatk Re: Random DTC41 Tip
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Grounds are super important. Good tip.
Posted on: 6/25 19:19
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1989 Corvette...custom 383 stroker, superrammed and cammed, built trans with PeteK 2800 stall. Mustang dyno results: 336 rwhp / 419 rwtq.
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hcbph Re: Random DTC41 Tip
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Had it reoccur today for maybe 20 sec. Not near as many times as before but still happened. I'll have to start looking at additional grounds, though these should not have to go onto a lift to get to.
Posted on: 6/27 23:52
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hcbph Re: Random DTC41 Tip
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Don't know if it's the answer or not but found something definitely wrong. The ecm had been removed in the past and was just shoved into place and wiring harness pulled below it to hold it into place. I fastened it in and added a ground wire to insure a good ground with the case.
Ran it for 5 miles and ran fine but then again it's done that before. Have to take it for a longer drive and see what happens.
Posted on: 6/30 22:50
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bogus Re: Random DTC41 Tip
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DTC41, loss of communications, right?
Posted on: 7/1 0:03
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j3studio Re: Random DTC41 Tip
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Quote:

bogus wrote:

Grounds are so important on plastic cars!

Lordy, yes.

Posted on: 7/1 19:04
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hcbph Re: Random DTC41 Tip
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Quote:

bogus wrote:
DTC41, loss of communications, right?

Yes it is. If this isn't it, I guess it's time to go into the distributor next. I'm hoping the lack of a good ground on the ecm is the problem, if not then onto the next area.
Posted on: 7/2 0:51
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bogus Re: Random DTC41 Tip
Grand Imperial Pooh-Bah
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DTC41 is the comm error... this means the UARTs are failing.

UART - Universal Asynchronous Receive Transmit - are chips that send and receive data from the ECU to the CCM and from the CCM to and from the EBCM (brakes/ASR), the AC system and the radio.

There are two distinct UARTs on both the PCM and the CCM, they merge into 1 wire and split again on after the firewall... this creates a redundancy, if one fails, the other will take over.

I don't have the time now, but I will check the Helm Manual on this schematic for this... it used to be a tan wire, but I don't know the details on a 96.

At this point, I don't think the ground is the main problem... it smells like a failing PCM...

Posted on: 7/2 15:54
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hcbph Re: Random DTC41 Tip
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I'm going to keep looking but I've got an appointment with my mechanic in a week in case I can't find it. As a former IT guy, I hate computerization in cars.
Posted on: 7/4 6:14
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bogus Re: Random DTC41 Tip
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I am an IT guy... I don't mind computers in cars, I just hate computers in cars where they are nothing but maintenance fails...

Engine controllers, IMHO, are the best thing since sliced bread... thanks to the tech (which came to the street from F1 racing), has given us 700hp V8s that can get 20 mpg on the highway... The 400hp LS2 in my '06 Coupe gets nearly 30 on the open highway!!! The LT1 in the C7, when mated to a 7spd manual, set in eco-mode, will hit nearly 40 MPG on the highway. That's insane. And if it helps us sustain our passions, I am all for it.

Where computers become a pain in the ass is when the OEM stops supporting them. I spoke to Harlan Charles about this a few years back, asking if GM was considering supporting older Corvettes with hard to get parts and he indicated it was on the radar, but I suspect the C8 kinda slowed that plan.

We in Corvette land are not the only ones with this problem... The Ferrari 348, 1990-1994 or so... it has a computer module that manages the climate controls. This component was made for Ferrari, using Ferrari specs, by an outside vendor. The downside? This module fails and you are stuck with an expensive car with no heat or AC! Ferrari doesn't make the part (well, they may now), and won't let the vendor make it, either... As I understand it, there is a dude in San Diego that fixes them... however, my point is that we are not alone.

In general, the computers in a C4 are pretty good. The CCM and EBCM are noted to last forever, and the ECM is good to 150k miles or more... Even tho it is made to deal with engine heat, I don't think it lives as long as it would if it was in a cooler area. Why not put it in the back storage bin? As an aside, if you need an ECM, the 1992 and 1993 Corvette ECM is shared with the 1993 Camaro/Firebird LT1 ECM. There are 120k of them out there... just swap the chips.

Do NOT trust the rebuilders... they don't know what they are doing...
Posted on: 7/4 16:16
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