I'm new to C5 forum as I drive a C6 and usually hang out there, need a little help for a friend of mine. He came by last night with his newly purchased '98 C5 Auto with 45K miles on it. Said he was having a shift problem, we took it for a ride, the transmission shifts VERY HARD from 1st. to 2nd. gear, the whole car jumps, not smooth at all. Other gears are fine, from 2nd. to 3rd. and 3rd. to 4th. are smooth (I assume this is a 4 speed auto) and all the downshifts are smooth, even from 2nd. to 1st. is fine. His horn doesn't work and the dealer said the problems might be electrical and might be related (sounds like BS to me), my friend is taking it back for the horn issue next week. Any idea's about the transmission issue, he (and I) know nothing about the workings of the trans, could it be a simple band adjustment or fluid change, any help would be appreciated, thanks in advance.

 

Did he buy it from the dealer? The trans should not shift harsh from first to second. He needs to first check the fluid level. My vette shifts smoothly through all gears.

 

Yes, bought it from the dealer who told him he (the dealer) test drove if and found "no problems"......

 

Check for DTC's with the DIC

If you find P1870, and I bet you do, clear it and see if the trans shifts smoother.

The DTC is for "Transmission Component Slipping" and when present, the PCM tell the trans to have high line pressure and the 1-2 shift can become brutal.

Do some research on P1870.

Another possibility is that someone may have tuned the trans **** properties.

Ron

 

Excuse my ignorance, is there a way to check for "DTC's" (I assume some kind of diagnostic trouble code) using the DIC or do you need some kind of diagnostic tool? Thanks...

 

C6 guys.........

DIY Service Techs are going to be most interested in the LPG’s ability to show diagnostic trouble codes (DTC) for all the modules that transmit them.

The "diagnostic display" mode is entered with the following Procedure: Page 8-500

1) Turn on the ignition but don't start the engine.
2) Press the "reset" button to turn off any warning messages
3) Press and hold "options" and
4) While holding "options", press "fuel" four times within a 10-Second period.

Initially, the on-board diagnostics go into the "automatic" mode, which shows each module's DTCs in a
pre-set sequence: (Page No. are for the GM Service Manual)
10 PCNI Powertrain Control Module page 6-357 - 6-361
28 TCS Traction Control system ABS on page 5-86
?? RTD Real Time damping page 3-136
40 BCM Body Control Module page 8-405 LTD Page 8-727
60 [PC instrument Pane! Cluster page 8-508
80 radio page 8-213
99 FIVAC Heater Vent-Air Conditioning page 1-118
A0 LDCM Left Door Control module page 8-904 to 8-951
Al RDCM Right Door Control Module page 8-904 to 8-951
AC SCM Seat Control module page 8-1064-8-1082
B0 RFA Remote Function Actuation page 8-676

For each module, all DTCs will be displayed. If none are present in a module, you will see "no more codes" on the ICP display.
There are two kinds of DTCs, "Current" and "History," designated with a letter suffix, "C" or "H". A current code indicates that the malfunction is present in the system whose module is displaying data. A history code indicates a problem existed in that module sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it is possible it's evidence of a previous problem. Now solved, that was not removed by clearing codes. More likely is that a history code indicates an intermittent malfunction.

"Intermittent" are the most challenging DTCs. An intermittent may have happened only once, may have happened more than once but is inconsistent in its appearance or may be happening on a regular basis but not at the time the IPC is displaying codes. History codes can also be caused by a current malfunction in a system that is not Operating at the time DTCs are displayed. An example is the rear window defogger, which doesn't operate until the BCM detects engine rpm. For history codes set by a system that does not operate with the key on and engine off, a special diagnostic tool called a "scan tester is necessary to properly diagnose the malfunction.

Once the IPC has displayed all 11 modules, the system goes into the manual mode, which allows selection of each module, using combinations of DIC buttons. The manual mode can also be entered at any time during the automatic sequence by pressing any button except "E/M". Once the IPC displays "manual diagnostics", you may select a particular module by pressing the options button to go forward or the "trip" button to go back. Once a system is selected and a DTC is displayed, if more than one are present; press "gages" To move forward or "fuel" to go back. To exit the diagnostic mode at any time, press E/M". If you want to erase or "clear" codes, press "reset". Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory.

 

Thanks Ron, I'll print this out and give it a go!

 

Good luck!

 

MIL on? P1870 will turn it on when that sets. Not all codes do, but will show up using the DIC as described above. There's a pressure control solenoid related code that might have a similar presentation that doesn't turn on the MIL.

You may want to clear codes through the DTC. (Make note of anything you clear.) Some will cause the PCM to enforce certain conditions and it can be helpful to clear them and see what changes. E.g., your 1-2 harshness may go away but quickly return along with a code or two. You need to see how things are behaving before the PCM starts clouding the issue, if it is.

 

Topless is correct. Check Engine Light, should be on.

On my car, the error was present, but some previous owner had it tuned out......

HPT or EFI live can be sneaky that way!

Ron

 

Regarding detecting any performance tuning if you're worried about that, look for easy to spot evidence like fan turn on temps. If they don't turn on at stock temps, tuning is almost certain. If they did that other stuff is likely too. Conversely, if they do operate at stock temps performance tuning is unlikely. There are more definitive ways to detect it, but this is an easy, although not certain, method.

 

If I was your buddy before getting the "dealer" to do cash work on the car (it's never under their warranty you know) I'd have Carmen or Dennis at the "Vette Drs" (in Amityville, NY) check the car for a previous tune to see if that is the main issue. As an added bonus, they are knowledgeable in the C5 in all aspects.

 

Have them diagnose and repair.

 

Thanks to everyone for the great info, I'll be talking to my friend and I'll let him decide what he wants to do. I think right now he wants to give the dealer a chance to fix it first with no cost to him (my friend), I just want to do a half a** diagnosis so at least he's got some kind of info in case the dealer tries to BS him, thanks again to all!