The procedure described here works for all systems with diagnostics on the R129 through model-year 1995 except for the SRS (airbag) for '94 and '95. On some of the systems from '94 and '95 it will not retrieve as much information as an advanced scan tool would.
Each system's diagnostic output signal is wired to a specific socket of the car's main "diagnostic connector", X11/4. An additional pair of sockets in the connector provide battery voltage and chassis ground for convenience. Early cars with continuous-fuel injection have 16 sockets (picture), while later models have 38 sockets. The sockets are numbered for easy identification. When you make connections to any of the you should know that all circuits have protected outputs and nothing can be damaged by mistakes.
Codes are read sequentially one at a time. That is, you trigger the system you are checking to issue a code, you read the code, you trigger another code, and so on. With the key on and engine off, you trigger a code by electrically shorting the system's particular diagnostic socket to ground for 2 to 4 seconds using a wire. A second or two after the wire is removed, a series of electrical pulses will occur at the socket. The number of pulses corresponds to the number of a code.
There are numerous ways to view the pulses for counting and getting codes. The simplest method is to connect a 99-cent LED from Radio Shack (P/N 276-209, pictured) between battery voltage and the socket of the system being checked (the one you ground for 2 to 4 seconds to get a code) and watch it blink in sync with the pulses. A pair of banana plugs is nice for this. Be sure to have the polarity of the LED correct -- if it is wrong, you won't damage anything, but the LED won't ever turn on. In the special case of reading top controller codes on cars made through 12/93, you don't even need the LED -- just watch the top control switch on the console flash. This is possible because one side of the lamp inside the switch is wired to the diagnostic socket for the top control system.
Once you have read all of the codes you can erase them. They are erased individually one at a time. To do this, read a code, wait a few seconds, and then short the diagnostic socket to ground for 6 to 8 seconds.
For a list of diagnostic codes see post #3 below.
For diagnosing convertible top problems I believe it is best to read/erase all codes and then operate the top. When the problem occurs, continue holding the top control switch until it flashes or 80 seconds elapse -- whichever occurs first. Then read the freshly stored codes.
Each system's diagnostic output signal is wired to a specific socket of the car's main "diagnostic connector", X11/4. An additional pair of sockets in the connector provide battery voltage and chassis ground for convenience. Early cars with continuous-fuel injection have 16 sockets (picture), while later models have 38 sockets. The sockets are numbered for easy identification. When you make connections to any of the you should know that all circuits have protected outputs and nothing can be damaged by mistakes.
Codes are read sequentially one at a time. That is, you trigger the system you are checking to issue a code, you read the code, you trigger another code, and so on. With the key on and engine off, you trigger a code by electrically shorting the system's particular diagnostic socket to ground for 2 to 4 seconds using a wire. A second or two after the wire is removed, a series of electrical pulses will occur at the socket. The number of pulses corresponds to the number of a code.
There are numerous ways to view the pulses for counting and getting codes. The simplest method is to connect a 99-cent LED from Radio Shack (P/N 276-209, pictured) between battery voltage and the socket of the system being checked (the one you ground for 2 to 4 seconds to get a code) and watch it blink in sync with the pulses. A pair of banana plugs is nice for this. Be sure to have the polarity of the LED correct -- if it is wrong, you won't damage anything, but the LED won't ever turn on. In the special case of reading top controller codes on cars made through 12/93, you don't even need the LED -- just watch the top control switch on the console flash. This is possible because one side of the lamp inside the switch is wired to the diagnostic socket for the top control system.
Once you have read all of the codes you can erase them. They are erased individually one at a time. To do this, read a code, wait a few seconds, and then short the diagnostic socket to ground for 6 to 8 seconds.
For a list of diagnostic codes see post #3 below.
For diagnosing convertible top problems I believe it is best to read/erase all codes and then operate the top. When the problem occurs, continue holding the top control switch until it flashes or 80 seconds elapse -- whichever occurs first. Then read the freshly stored codes.
