Question: Ref:Paper Clip Method/Code Retrieval?

[Donne Trav]

It has been mentioned that a "paper clip" can be used to retrieve codes on
the '94 LT1 engine, connecting the "4 pin" and the "12 pin". Question: where
are these "pins" to be found? Is there any chance of "low voltage" shock? This is all new to me. Thankyou.

 

[Hib Halverson]

You cannot use the paper clip method to retrive ECM codes on a 94. Only on 81-93.

You can retrieve codes from the CCM and the ETBCM by connecting pins 9 and 12 together and watching the display on the IP cluster. Detailed instructions on "CCM Diagnostics" are in the factory service manual.

The diagnostic linke connector (DLC) containing the pins is under the instrument panel above your knees. It's shaped like a trapezoid.

Information on how to interpret the codes and diagnose the problems behind them along with a diagram of the DLC are all in the factory service manual.

 

[Donne Trav]

You cannot use the paper clip method to retrive ECM codes on a 94. Only on 81-93.

You can retrieve codes from the CCM and the ETBCM by connecting pins 9 and 12 together and watching the display on the IP cluster. Detailed instructions on "CCM Diagnostics" are in the factory service manual.

The diagnostic linke connector (DLC) containing the pins is under the instrument panel above your knees. It's shaped like a trapezoid.

Information on how to interpret the codes and diagnose the problems behind them along with a diagram of the DLC are all in the factory service manual.

Is there a connection to be made, or is some other instrument involved?
Thanks for your reply Mr. Halverson.

 

[Hib Halverson]

You make a jumper wire then connect pins 5 and 12 then turn on the ign. The IP display will show any codes which are stored in the modes it supports. I believe it's the CCM, EBTCM and SIR.

Best bet is to read the factory service manual. It has an entire subsection on using CCM diagnostics to show CCM and EBTCM codes. You really can't effectively diagnose and repair the electronics on a 94 without that book.

As for "another instrument" being involved...yes, you can, also, use a "scan tester" to read codes. Testers which read ECM codes are relatively inexpensive and the only way you can read ECM codes on 94-96 is with a tester. Scan testers which read CCM and EBTCM codes as well as ECM codes are quite costly. There is also scan test software available which runs on notebook PCs.

Diagnostic equipment is covered in a series "Corvette Enthusiast" magazine has been running over the last year or so. Part 4 of this series has just published in the May 09 issue and Part 3 published in the Mar 08 issue). Both those parts covered scan testers and scan test software.

 

[Paul Higg]

Donne, you CAN use a paper clip to pull codes on a 94 because I HAVE one. Pins 4 and 12 need to be jumped. At knee height on your right knee you will see a plug. As you are looking straight at it count from the top row over from left to right where the top left is #1 and follow it down to the bottom row. Pins 4 & 12 are actually right on top of each other.

If you want you can PM me and I will give you all the information you need. I will also give you my cell # to walk you through it and I will tell you what the codes mean as I have an FSM for a 94.

Paul

 

[Hib Halverson]

Paul is correct.

You can "pull" codes (more properly, "diagnostic trouble codes" or "DTCs") from 94s with a paper clip or a jumper wire by grounding pin 12 of the DLC, but....the codes you get are via "CCM Diagnostics" rather than the flash-code diagnostics used with 81-93s. I said earlier that 94s and 95s won't send ECM data via CCM diagnostics, but I think that both Paul and I are, both, "right and wrong". I apologize for misleading you but 94s and 95s are a bit unique on ECM diagnostics and I had forgotten that feature of those systems.

First, with the exception of perhaps a few very early 94s assembled with 93 engine controls systems, 94s do not support "flash code" diagnostics for ECM codes.

Why?

Well....during 94 and 95, Corvette was part of GM's "early roll out" of OBDII (stands for "on-board diagnostics generation two" which was required starting in 1996. As a result, the 94/95 ECMs have partial OBDII capability and that eliminated the ECMs ability to flash the check engine light. In addition, the fault code info generated by that partial OBDII capablility is not acessible via CCM diagnostics because OBDII mandated four digit fault codes which can't be displayed on the car's IP.

I, also, implied in earler poats that the CCM ability to display "module 4.1", which are ECM/PCM DTCs, did not exist. That's "partially" wrong. The CCM from MY94/95 will display the two-digit DTCs generated by the OBD part of 94/95 system. What it won't display is the DTCs generated by a 94/95's "partial OBDII" capability and, again, that's because OBDII codes are four digits rather than two and the IP only can display two digits.

Consequently, the only way to read two-digit ECM codes from a 94 is by CCM diagnostics and you enable that by connecting pin 12 of the DLC to ground (either pin 4, pin 5 or other grounding point) then turning on the key. The full procedure, including how to read the codes by manual selection of the modes, is a bit long and Paul Higg has already volunteered to PM you the details or let you call him.

Lastly, to read the four digit DTCs sent by the OBDII part of a 94 ECM requires a scan tester.

Again, I apologize for the confusion which must be even more frustrating to somone who's trying to diagnose a 94 for the first time.

Good luck.

 

[vdogamr]

Which pins?

In the top 4 posts of this thread there are 3 different pin connections mentioned. (4&12, 9&12, and 5&12) Which pins do you actually use? Is it different for different years? Not to be selfish, but I have an 88, what pins do I use? Are you telling me that the display will digitally show a code number?

(I got my first "Service Engine Soon" light this morning. hnoes)

Thanks

 

[Hib Halverson]

The above discussion is completely irrlevant to an 88.

To get ECM codes from the 88, you use flash-code diagnostics. The 88 neither has the 16-pin DLC nor does it support displaying codes on the IP.

With an 88, you have a 12-pin connector. Ground the diagnostic pin B by either connecting it to pin A or another ground source then turn on the ign. but do not start the engine.

Once you enable flash code diagnostics, the MIL comes on for 4-seconds then blinks two digit DTCs. Each digit is signified by half-second-apart flashes. One second separates the digits. Codes flash three times with a 3-sec. pause between. If multiple codes exist, they'll display lowest to highest. Each code or code string is bracketed by code 12, signifying the sequence's start and end. If the MIL only flashes code 12, no DTCs are stored. If the MIL is on, but no codes are stored, see the FSM.

Say DTC22, a throttle position sensor fault, is present. The light flashes once, then twice (12), three times in succession. Next, it flashes twice, then twice (22), repeating that three times. Finally, it flashes code 12, again, three times in succession. It looks like this: 12-12-12-22-22-22-12-12-12. The sequence repeates until the jumper is removed.

For more detailed information, read the 88 Factory Service Manual.

Good luck.

 

[gmhowe]

Or just take the car to Auto Zone or Checker and they will check the codes for you and its free.

 

[Paul Higg]

Hi gm,

They will check them at those auto parts stores on those models. But the 94/95 which is what mine is, is a kind of "bastardized" plug. It is a real ODB II plug but you cannot read codes with an ODB II scanner. I read somewhere that you could with an adapter and a guy at Advance Auto told me they actually had an adapter for the scanner but they were told to pull the adapter. Reason unknown.

On mine I always use pins 4 & 12 per the FSM.

Paul

 

[starbuck]

Now I'm confused.
I have a 95. There is a code reader available form Harbor Freight
Harbor Freight Tools - Quality Tools at the Lowest Prices
that I was going to buy. Will this thing work on a 95 or is there some kind of adaptor I'll need or a different unit all together?
I'd rather not spend a zillion dollars on a simple code reader if I can avoid it but I'd like access to the knowledge.

 

[Hib Halverson]

Hi gm,

They will check them at those auto parts stores on those models. But the 94/95 which is what mine is, is a kind of "bastardized" plug. It is a real ODB II plug but you cannot read codes with an ODB II scanner. I read somewhere that you could with an adapter and a guy at Advance Auto told me they actually had an adapter for the scanner but they were told to pull the adapter. Reason unknown.

On mine I always use pins 4 & 12 per the FSM.

Paul

The 94s and 95s do not have a "bastardized" plug. The 16-pin DLC is the same on those cars as was used on the "full" OBDII 96-09 Corvettes and all other GM cars which have 16-pin connectors.

The difference is in the ECM calibration itself. Read my above post which describes GM's "early roll-out" of OBDII. I'll add: there were three other platforms (C, H, U) in 94 and another five platforms (G, J, F, G, S/T-truck) in 95 that were part of this program. Another thing I should add about the early-rollout was that, when any of the OBDII codes would set, they would not turn on the check engine light. The system was set-up that way because all GM wanted was to gain some field experience with OBDII. What it didn't want was customers coming in with MILs on caused by a fluke or a malfunction in the then-under-development OBDII. On a 94 or 95, if the MIL came on, it was because a two-digit code stored by the OBD system turned on the light. When a customer came in for service with the light on, dealers were instructed to read any of the OBDII codes where were also set and pass the info on to GM. That gave GM the field experience they needed. The early-roll out was a great idea and gave GM needed OBDII diagnostics experience as much as two years ahead of the 1996 implementation deadline that some other manufacturers might have lacked.

The "code reader" sold by Harbor Freight may not be compatible with a 94 system and, even if it is, it will only read the codes held in the memory of the partial-OBDII diagnostics. It will not read the codes in the full OBD section of memory and those are the codes which turn on the MIL.

You may be able to use some other consumer scan testers which support 81-93 ECMs by adding a 12-pin-to-16 pin adapter. I do not know where you can obtain such a device, but I'm sure they exist. I'd check with the manufacturer of the scanner. Also, some consumer scanners come with, or have available as an option, a special cable for OBD systems having 16-pin connectors. In addition, there are some software-based testers (such as "EASE") which come with such cables.

Most professional-level scanners (TECH1A, TECH 2, Mastertech, etc) either will have such an adapter or allow you to connect directly to the 16-pin connector yet read OBD codes...as well as the OBDII codes that might be in memory of those systems.