Sprinter 4WD Conversion Idea, GMT-800 IFS.

[luthj]

On a software related note, I cam across the canbus status frames for Jeeps which use the NAG1 transmission. The trans shifts differently, and ignores 1st gear in low range (and uses the higher reverse gear R2, which is normally not selectable).

So I wrote a couple lines of code to send these can frames to the TCM, just to see what would happen. Surprisingly the sprinters TCM was actually recognized the frames, and did some strange stuff.

First off, it shows R2 when I select reverse (via scanner live data). In drive it shows 2nd, and no first.

Actual driving gets kinda weird. Sometimes its starts in 2nd (lots of TC slippage), sometimes it doesn't. It randomly through a "gear implausible code", and sometimes just goes to "fault" without a relevant code. The dash display just shows D, and won't show the selected gear when I force a downshift.

So the good news is that the TCM contains a low range specific program. I just need to figure out how to access it.

As a note, When I send these frames to the ESP module, it freaks out, and throws a "invalid Variant coding", which means I am on the right track, cause its seeing the 4WD status frames, but the van isn't equipped with 4wd.

What I need to do from here.

• Log CAN frames to see if another device uses the same ID. If so, I need to modify those frames, not transmit my own.
• Figure out which frame I need (there are two I am working with).
• Calculate that low range ratio the TCM expects. From there I can adjust my program to correct it the wheel speeds to (2.73/XXXX) to prevent gear implausible codes.

Here are the frames I am playing with


0x428 with payload {0x01, 0x00, 0xff, 0x03, 0x7a, 0x00, 0x00};

0x218 with payload {0x80, 0x00, 0x00, 0x58, 0x20, 0x80, 0x36, 0x22};

 

[luthj]

Okay, I think I found the issue.

First-
Frame 218 is currently in-use on the sprinter. So I need to modify these existing frames. I think they are shifter status frames?

Second-
I thought I needed to send the whole payload, but it turns out I only need to modify the 4th byte to 0X58

Third, I don't know if I need frame 428 or not. Need to do some testing.

 

[luthj]

Looking at the 218 frames, it looks like the 3rd byte might be the Selected and current gear. "DD" Of the K-line PIDs used to diagnose the TCM, 0x30 reports the current gear with D=park and 1-5 being requested gear. So I need to do some testing. With the right byte values in this frame, I think I can command the trans to any rational gear.


source port, FrameID, Payload:

1,218,80:00:DD:48:23:80:33:21:,
1,218,80:00:DD:48:23:80:32:22:,
1,218,00:00:DD:48:23:00:35:23:,
1,218,00:00:DD:48:23:00:34:24:,
1,218,80:00:DD:48:23:80:35:25:,
1,218,80:00:DD:48:23:80:31:26:,
1,218,00:00:DD:48:23:00:38:27:,
1,218,00:00:DD:48:23:00:33:28:,
1,218,80:00:DD:48:23:80:32:29:,

 

[shade]

It randomly through a "gear implausible code"

I think you're onto something.

 

[luthj]

I wondered how long it would be before this thread got a Hitchhiker's guide reference.

Kinda like a fantasy version of Godwin's Law?

 

[luthj]

A bit of deciphering with some help from the internet and friends.

Frame 230 is the shifter status. Its just 1 byte long.

0x230 1
08-PARK
07-REVERSE
06-NEUTRAL
05-DRIVE
0A-DOWN
09-UP

218 is the TCM status Byte 3 is the target and current gear. There is lots of other stuff going on in that frame. It jumps around a lot though, so it could be a sequence. Groups of 218 frames are sent back to back, with bytes 1 and 6 being 80 or 00, which may be some kind of status or reply requested.

D=park
B=Reverse
0=neutral
1-5= 1st-5th



The TCM also sends 338 and 418 Frames. 418 also contains the target and current gear, and some other data.

 

[luthj]

I still haven't gotten a final back from my last laser quote request. I did a couple of web based quoting tools, and using A36 it was ~500$ (without shipping and tax). If I can't find a local place with a decent quote, I may just end up dealing with the freight cost. It shouldn't be this hard, but apparently it is.

 

[shade]

I still haven't gotten a final back from my last laser quote request. I did a couple of web based quoting tools, and using A36 it was ~500$ (without shipping and tax). If I can't find a local place with a decent quote, I may just end up dealing with the freight cost. It shouldn't be this hard, but apparently it is.

I guess that kind of work hasn't transitioned to a web based marketplace. Come to think of it, I know some local shops by word of mouth, but searching online is a joke. Even if the logistics of getting material and finished parts moved is a pain, CNC machining and software standards make it much easier to take small jobs like yours.

 

[luthj]

There are at least 10 shops within 15 miles of me that offer laser cutting services. I have contacted 6 of them now. One overpriced quote is all I have seen thus far. I have 2 quotes to follow up with on Monday. It should be an easy job that makes them 200-300$ for maybe one man hour total between setup and programming. ?‍♂️

 

[shade]

There are at least 10 shops within 15 miles of me that offer laser cutting services. I have contacted 6 of them now. One overpriced quote is all I have seen thus far. I have 2 quotes to follow up with on Monday. It should be an easy job that makes them 200-300$ for maybe one man hour total between setup and programming. ?‍♂️

My guess is they're already busy with bigger jobs, and they aren't hungry enough to put your little job on the table.

 

[luthj]

My guess is they're already busy with bigger jobs, and they aren't hungry enough to put your little job on the table.

Your probably right. Such is the boom and bust of fabrication services.


On tangential note, I have some switches, LEDs, and holders on order. I also need to place an order for some multi-conductor marine wire. My plans are to make a head up 4WD indicator panel, though I may put it on the center console. I will have a switch and indicator light for the front axle disconnect. My wire stocks are basically down to scraps after the conversion, so I probably need to order a few 100ft rolls for common single sizes, and a few 35-50ft rolls of the combination cables.

 

[shade]

Problem solved. I'm not sure how you upload your files, though.

 

[luthj]

If I was in a permanent abode with a decent sized shop, I would just pony up for a decent CNC plasma table (4x4ft). They are not very expensive, and can cut 3/16 steel plus/minus 1/16" accuracy.

 

[shade]

Any maker shops near you? I just looked, and there's one on FB that has a laser table.

Nevermind, 1/4" plastic.

 

[luthj]

Yeah, I would be regular at a maker space with a 4kw laser... though I may have to join to use the lathe.