Chart B-3 and B-4 No Communication

Chart B-3 - No Communication:

Wiring Diagram For Charts B-2, B-3, B-4, B-5 & B-6:

CHART B-3 - NO COMMUNICATION

Circuit Description:

Since both the CRT and the IPC are unable to communicate with the BCM, the data line must be shorted to ground, the data line has two opens, or the BCM is not communicating.



Test Description:

1. If the problem is a short in the data line, breaking the data line apart, trying to get the short out of the line, will be indicated by communication being restored to those devices left on the line. By removing the ALDL cover and disconnecting the programmer, we can eliminate the ECM, Programmer, and CKT's 800E, 800C, and 800B from the data line. If the "Electrical Problem" telltale goes off, the problem was in what was disconnected.


2. If the "Electrical Problem" telltale stays off when the ALDL cover is replaced, the problem is that the programmer lost its ground path and stopped all communication, or, the programmer is bad.




3. If the "Electrical Problem" telltale comes back on when the ALDL cover is replaced, disconnecting the ECM will indicate if the problem is the ECM or CKT's 800E, 800B, or 800C. The ECM is at fault if the "Electrical Problem" telltale goes off.

4. If the "Electrical Problem" telltale stayed on when the ALDL cover was removed and the programmer was disconnected, disconnecting the CRTC will also eliminate the CRTC and CKT 800F. Because the "Electrical Problem" telltale will light if either IPC or CRTC lost data, watch the speedometer display to determine if communication is present. Zero in the speedometer display indicates the CRTC or CKT 800F is at fault.


5. To determine if the CRTC or CKT 800F is at fault, jumper the data line together at the CRTC. If the speedometer displays zero the CRTC is at fault.

Chart B-4 - No Communication (Cont'd):

CHART B-4 - NO COMMUNICATION (CONTINUED)

Circuit Description:

Because the system is still not communicating, when everything except the BCM, IPC, and CKT's 800A, 800H, and 800G are left, the problem must be with one of these.


Test Description:

1. Measuring voltage at the ALDL will determine if there is a short in what's left on the data line. If 1 to 6 volts are present, there is no short.


2. If the "Electrical Problem" telltale in the IPC stays on when a jumper is placed between the ALDL and the CRTC connector, the BCM is at fault. If the telltale goes out, there are two opens in the data line and this jumper will correct the problem.


3. If the voltage, when measured at the ALDL was below 1 volt or over 6 volts, removing the IPC and rechecking the voltage will indicate if the short is in the IPC and CKT 800G. A reading of 1 to 6 volts indicates that the short is in the IPC or CKT 800G.


4. If the voltage, when measured at the ALDL with the IPC removed, was below 1 or above 6 volts, disconnecting BCM Connector # 3 and rechecking the voltage will indicate if CKT 800H is shorted. If voltage is between 1 and 6 volts, CKT 800H is shorted. If voltage is above 6 or below I volt, CKT 800A is open or shorted, or the BCM connector, or BCM is faulty.