LouisvilleLT4

I am posting this to clear some things up about the "paperclip" trick as it applies to later model C4's ('94-'96), and I just want to make sure nobody is in the dark about all the various features of their car's built-in diagnostic mode. I will show that it does a lot more than display codes (it's got a menu!), and I will show you what the "SYS" message means, and I also hope to clear up some major misinformation.

Specifically, there have been numerous rumors that the 1996 cars have no diagnostic mode. You can enter the '96 diagnostic mode, but the rumors say it's only a holdover from previous years and that everything shown on the screen is garbage. This is false. The 1996 cars DO have an elaborate and functional diagnostic mode, with only one major change.

Our cars have numerous computers (it calls them "modules") networked together, one of which is the PCM, which controls the engine. The root of the rumors lies in the fact that in '96, new laws mandated the PCM's protocol to change to OBD-II, which used a standardized four-digit numbering scheme for "check engine" codes, which is too big to fit on the LCD. Rather than find some other way to display that many digits, GM decided to say screw it and deleted the functions that read/clear PCM codes from the diagnostic mode. The PCM simply no longer shows up at all among the modules listed.

They forgot to mention this little tidbit in the service manual, which confused a lot of people into thinking that the whole CCM chapter does not apply to '96 cars, but other than that one detail, it does. GM did not change any of the functions involving other modules (CCM, EBTCM, etc), nor did those functions get corrupted by the switch to OBD-II; they all still show up and function correctly. Thus the majority of the diagnostic mode's power is still there in '96. I know because I checked.

-----Using diagnostic mode-----

To enter the diagnostic mode, you simply ground the diagnostic pin on your car's diagnostic connector (located near the driver's knees). Various DLC connectors were used throughout the C4's life, all with different pinouts; on '94-'96 cars, you connect the fourth pin from the left in each of the two rows of pins to one another, with a paperclip or some other conductor.

When you turn the ignition to "run," you will now be in diagnostic mode, which uses the LCD screen and the DIC (driver information center) buttons for input and output. You may start and drive the car while in diagnostic mode; in fact, the car has to be running for some of the functions to be meaningful. The only disadvantage is you will not be able to see your normal gauges while in this mode since the LCD screen will be in use.

When you start diagnostic mode, the LCD will show you any codes stored in the car's various computers. In '96, Module 1 is the CCM (main/dash computer), 4 is the PCM (engine computer, doesn't show up in '96), 7 is the RTD (computer-controlled shock absorbers, if you've got them), 9 is the EBTCM (antilock brake and traction computer), and A is the DERM (air bag computer). These are cycled through one at a time, with dashes indicating the end of codes for that module. A "C" prefix means the code is currently active, meaning that the relevant parameters are out of range right now; an "H" means the code has been stored in history but is not currently active.

Unlike the car's other electronic systems, such as PCM, ABS, air bags, etc., there is no specific "CCM" lamp to indicate a malfunction when one is present. Instead, the CCM flashes the word "SYS" three times every once in a while on the LCD whenever there are active CCM codes present. If the code thrown is one that involves only the security system, the "SECURITY" lamp will illuminate instead, or they will both flash together if it involves the Fuel Enable Data Stream.

Upon entering diagnostic mode, as mentioned, you will first see a listing of diagnostic codes for each module. Afterwards, you will enter the menu (or you can press any information center buttons to skip to the menu). Did you know there was a menu? I didn't, until I read the FSM.

You'll know you're in the menu when you see the number "1.0". The first digit, before the decimal point, refers to which module you are talking to at the moment, as numbered above. The second digit indicates the menu item. Item .0 means that computer is awaiting instructions. Item .1 displays any codes for that module and .7 clears them. This applies to all of the car's computers/modules. Note that any non-CCM codes will always show up with the "H" as in history, since the CCM does not know whether or not they are currently active.

The CCM has additional options on top of these; .2 and .3 let you cycle through the CCM's stored data and inputs, respectively, and option .4 lets you toggle each of its outputs manually (this part is fun).

To navigate the menu items, use the "gauges" and "trip odo" button. To navigate to the next or previous module, hold down the "fuel" or "trip" button for a second. To select a menu item, press "ENG MET."

One thing that I recommend doing at this point, is see if you have any EBTCM codes stored (module 9 in '96), and then delete them. You will hear the brake pressure modulator valves near the EBTCM click as it resets, and you might suddenly feel that your brakes feel and work much better than before. This was the case for me; I had a lateral accelerometer code, as well as a code from back when my Opti died making the tachometer go crazy. Neither code has come back since I cleared them, meaning that the presence of codes alone was enough to severely effect how my brake functions.

Now for the fun part: The CCM data, input, and outputs. These are options .2, .3, and .4 in the CCM module menu, respectively. After selecting any of these, press "eng met" to go to the next value and "fuel info" to go to the previous. The selections are:


Display CCM Data (Mode 1.2):
01 - Fuel Level (Gallons, tenths)
02 - Dimming Potentiometer
03 - Ambient Light Sensor
04 - Rear Defogger Timer
05 - Vehicle Speed
06 - Pass-Key
07 - Ignition Voltage
08 - Switched Voltage
09 - Cluster dimming
10 - LCD backlight dimming
11 - Radio & Climate dimming
12 - LED dimming
13 & 14 - Vehicle configuration
15 - Oil monitor count
16 - CCM version

Display CCM input status (Mode 1.3):

1 - PassKey fuel
2 - English/metric status
3 - Door key switch
4 - Right Door ajar
5 - Left door ajar
6 - key in ignition but in "off" or "acc" position
7 - hatch ajar
8 - Power door unlock
9 - Power door lock
10 - Parking lights
11 - Rear defogger input (car must be running)
12 - Seat belt switch
13 - High beam switch
14 - Low oil level switch

These values are either "1" or "0," and when toggled, the new value will be appended on to the old value (01 means it was 0 but is now 1).

Cycle CCM Outputs (Mode 1.4):

Selecting these options will manually activate the lights and sounds the CCM produces.

1 - Change oil light
2 - Check gauges indicator
3 - Fasten seatbelt indicator
4 - Security lamp
5 - High beam indicator
6 & 7 - chimes
8 - LCD blanking
9 - Defogger relay
10 - Courtesy lamp
11 - Low oil lamp
12 - Theft relay
13 - DAB relay
14 - door ajar light
15 - Horns (This will actually beep the horns, watch out!)

So there you have it; you can now dazzle and impress your friends with your car's diagnostic features, as well as test any of the circuits and systems in the interior. Please correct any factual errors I have made in this post, and if you know of any information that would be useful to add to this thread, so as to make it a centralized source for information about the late model CCM, let me know.

DougSilver

Thanks for the useful information all in one place. I have a 95 which is sort of a transition between OBD I and II since the connector has 16 pins (like OBD II) but, as I understand it, the computer is still OBD I.

Doug

BrianCunningham

Yes, I've done the 'paper clip' method on my '95

which has the OBDII connector, but is still OBDI

LouisvilleLT4

Cool. If I understand right, all of this information applies to your 1995 car as well as 1994. On top of that, those years should still contain the PCM read/clear functions. The "OBD-1" or "OBD-2" label only applies to your PCM; you have lots of other computers ("modules") in your car as well, which function regardless of the protocol the PCM uses.

LouisvilleLT4

I ought to include the "change oil" light reset procedure in here since it relates to the dash interface. To reset the "change oil light," you must turn the ignition on but not be in diagnostic mode. Do not start the car.

Press the "ENG MET" button, wait a second, then press it again. Then, press and hold the "Gauges" button. The light will flash. Wait to release the button until the light stays off.

pianoguy

I'll be saving this thread - thanks!!

the blur

If you short pin #5 & #6 you can see the LTPWS codes. It you short them 3 times quickly, it'll reset the LTPWS.

jonecap

Very nice post...thanks for writing it up. I'll have to give this a try.

neat

If you hold down the up and down arrows for the fan speed for 10 seconds, the fan speed display will show '00'

You can then use the up and down arrows to change '00' to a bunch of numbers. At one time, I knew what they all were, but the only one I remember now is '16'

When the small display is showing '16' press the button with the picture of a fan on it. The small display will now show you what the ECM is seeing for engine coolant temperature, in degrees C. This will be different than your dash mounted gauge, and for those of us tuning cars the temperature the ECM is using is more important that was is displayed on the gauge.

Ajaste

great post, Many Thanks!!

Rathbone

This is like an "Easter Egg", if you know what I mean. Interesting trick. Any other Easter Eggs known?

samsonb

What years does that apply to?

LT4POWR

95wht6spd

Needs to be a Sticky if not already.

hgh pwr

I agree it needs to be a sticky,very useful post and I wish they were all like this thanks.

-=Tom=-

Tagged for future reference.

Thanks!

No Go

Thanks for posting!

Had 3 codes in the EBTCM...probably for years...all clear now.

Cool.

dry

Does anyone Know if this same data cam be seen on a 1989??

SunCr

It can't - the '89 has one main module/computer - the ECM. There isn't a CCM or Body Control Module and though ABS has it's own Module, it isn't linked to the ECM or the Diagnostic Link and a dedicated Tester is used/necessary (hard to come by these days) at the Module if you want to read it's built in diagnostics. Limited information is available from the Control Panel on cars equipped with Electronic A/C, but it doesn't use the CTS signal to control when it blows heat (which I don't think started until '96, though the CTS can be displayed from '90 up) and neither does it link to the DIC. Anyway, you're not going to see anything other than ambient via the outside air temp sensor on these Years and the built in diagnostics are pretty useless: Open and Short Failures of the Outside and Inside Air Temp Sensors; Open in the Temp Door Feedback and Model/Software Number are about all you'll get. '90 and above will tell you all of this plus when it's out of gas and then give you some binaries for what the key sensors are reading, where the temp door is and some other, more meaningful stuff. Read all about it in your Owner's and Shop Manuals.

dry

Oh Well Thanks anyway!!