The HHT was the predessessor to SDS and SDS runs diagnostics on early systems by running an emulation of HHT on its screen, complete with the crude graphics capable with a hand held.

One could probably buy a clone for what a used HHT would cost, but there were a number of tools that emulated the early HHT. I just sold an old CS2000 last week for $500. The AST retriever would also do the job. Sold one of those years ago. I have used a SDS since they first became available in about 2001. Before that is was the above two tools.

I used the Snap-On 2500 to try and diagnose a run rich problem on a 93 400E.

It's been a few years, and I can still clearly recall what it did NOT observe.

Ultimate problem turned out to be a failed fuel pressure regulator. IIRC, pressure was supposed to be around 52 lbs, with a vacuum port that would allow some float to the cut off pressure. Actual measured pressure was off scale at 110 lbs. The scanner had no parameter that would clue you into this information.

The scanner looked at the O2 sensor duty cycle, fuel trim, checked ignition for each cylinder, rpm, and gave some data on the ETA, such as % open. there were several other items, cannot recall anymore.

Initially, we were suspicious of the ETA, but the scanner returned nothing that would conclusively prove or disprove if that were the cause.

Jim

Dave was interested in the format of the error codes that were reported by the MT-2500. Did the scanner report fault code numbers? If so were they two digit codes or three digit codes? Were there any descriptions supplied for the codes read?

It did report fault code numbers as I recall. I think they were 3 digit, and they did follow up with an explanation.

Again, it has been several years since I used your unit, and my memory is a bit foggy on this.

I had lots of notes (including the numbers and explanations) while trying to diagnose the issues with the 400E, but I'm sure I tossed those after I sold the car.

I know if you plug it into cousin Susie's 95 E320 wagon, you'll be sure to find at least a dozen set codes. :)

Jim

Hanno has a new 95 E320 that has a check engine light on, I'm busy tonight but maybe I'll give him a call and see if I could drive up to his place tomorrow night and see if I get two or three digit error codes.

Hey guys, thanks so much for the assistance... much appreciated!

:)

Dave,

I spoke with Hanno and he is really busy until next week, I'll get up there on Monday or Tuesday next week but you won't have your answer (at least from me!) until then.

Sorry - Tim.

Dave,

Sorry I can't be more specific, but has been a while, and I must have burned out those brain cells.

Fortunately, Linda's 95 E320 wagon has been percolating along without any problems, so I have not had a need to check codes.....

Jim

Oh, now I see whats going on...I'm going to be the poster child for this experiment. Let's connect his car to house current and see if it results in any codes?:eek: I'd be glad to help in this investigation. Note that I don't have a CEL on at the moment, its amazing what a new wiring harness can do. Tim, see you early next week.

I'm on the hunt for an inexpensive Impulse Counter for my 87' 560 SL. After several phone calls I may have to hire an archeologist to find one.

I don't think house current will be required... but I've always been willing to do what it takes to get the job done so make sure there are some extension cords on hand!!

It would be nice to provoke one of the codes Dave is dealing with, I think we should disconnect the stop lamp switch and see if we get a "02" code which would indicate the scanner reports in two digit format or an "006" code which would be more granular and indicate the MT-2500 can interpret codes in the three digit format.

Forum member JimF has an excellent web page that details how to make an impulse counter from parts available at radio shack for under $20.

Look at menu item #2 and page all the way down to the last page.

http://pages.prodigy.net/jforgione/MB_S500.html

If you don't want to build one PM me your address and I'll send you mine.

Hey, that's nice. Thanks, Tim. Thanks to you, too, Jim. If I understand what I've read correctly, that is what is required for the 107s and 126s would be reading.

The HTT is a 'poor' tool . . quote from a senior MB tech . .

This table shows that it's not an "infallible" tool for diagnosing EA problems just as a normal scanner (AST Retreiver, etc) isn't. It give ambiguous codes as the table below shows.

The sub-codes are shown (and read if at fault) in subsequent DTCs in most scanners.

So if you think the "HHT" will point to the 'culprit', you'll be dissapointed!

PM sent, thanks so much.