Distributor Coil - Intermittent Code 51 or 52

Bulletin No. T 84-5 2
File In Group 6C
Number 77
Date Mar. '84
SUBJECT: INTERMITTENT DFI DIAGNOSTIC CODE 51 AND 52

MODELS AFFECTED: ALL 1982-1984 MODELS EQUIPPED WITH DFI

FIGURE 1 - DISTRIBUTOR CAP/IGNITION COIL:

FIGURE 2 - IGNITION COIL EXPLODED:

DFI equipped Cadillacs may set code 51 and/or code 52 due to loose or unattached distributor coil grounds. The code may also be accompanied by an engine stumble or miss, erratic ISC operation, and erratic fuel data panel operation.

The cause is a voltage transient that occurs when the grounds for the high tension side of the ignition coil open and arc.

The ground for the ignition coil secondary windings is provided by a black wire with an eyelet terminal inside the distributor cap cover. The eyelet is attached to the coil laminations by a coil hold down screw. The ground path goes from the hold down screw through the coil laminations into a stamped steel ground strap. The ground strap attaches to one of the front coil hold down screws and terminates as the "ground" lug inside the distributor cap. (See Figures 1 and 2.)

If the eyelet is not tight or if the strap is not securely attached by a hold down screw, the ground may open intermittently causing a spark and code 51 or 52.

If the Service Manual procedure does not correct the intermittent code 51 and if code 52 was not caused by a battery disconnect, repair the intermittent code 51 and/or 52 as follows:

1. Remove the distributor cap cover.

2. Remove the four coil hold down screws and lift the coil out of the distributor cap.

3. Locate the ground strap and verify that the hook is around a hold down screw.

4. Replace the coil, positioning the ground eyelet around a hold down screw. Tighten securely.

If no trouble is found at the coil, other areas to check are:

1. A loose ground wire at the three terminal connector to the distributor cap.

2. The ground wires and connections in the harness to the distributor base.

Look for a pin not mating to the coil connections in the cap or a loose screw at the capacitor hold down in the distributor base (the ground is under the capacitor bracket).
For warranty purposes, use labor Operation No. T6086 at .3 hours.