ALLANTE BATTERY DRAINS DIAGNOSIS IS PROCEDURES

MODELS AFFECTED: 1987-1988 ALLANTES

Some 1987-1988 Allantes may experience a condition of a dead battery. This condition may be caused by a shorted electrical component which will drain the battery when the ignition is off (inadvertent drains).

To repair this condition check for an excessive draw on the battery and isolate the component causing the drain.

- An ammeter should be used when diagnosing an Allante for a battery drain. The BCM should also be allowed an initialization charge. Both of these items are outlined in Serviceman Bulletin T-89-35, Group 8, and should be strictly adhered to.

- A parasitic drain of up to 50mA is considered normal, 30mA being about average. Any battery draw above 50mA, with ignition off and retained accessory power disabled, is excessive and indicates an inadvertent drain.

- Even if the normal parasitic battery drain is 50mA or less, a vehicle left static for three weeks or more may experience a deteriorated battery charge.

- Recharge and test battery before returning to customer.

DETETERMING THE SOURCE OF THE DRAIN

Once it has been determined that a parasitic drain in excess of 50mA exists, follow the procedure below to isolate the component causing the inadvertent drain.

1. A visual inspection of the vehicle should be conducted. Check for any unwanted lights on, motors running or switches/relays activating.

2. An ammeter should be hooked up at the battery per Serviceman Bulletin T-89-35, Group 8. This will allow monitoring of the current draw at the battery during diagnosis.

3. The ignition should be OFF, the deck lid, glove compartment door, console lid and both doors should be closed.

4. Access the fuse panel underneath the center ashtray. Systematically remove the fuses and circuit breakers one at a time until the current draw at the battery falls below 50mA on the ammeter. If the drain is on fuse 8 or 25, or on circuit breaker 24, go to those sections of this bulletin. Otherwise, continue to step 5. All fuses and circuit breakers should be returned to their respective cavities of the fuseblock panel.

5. Once the source of the battery draw has been identified, disconnect components on that electrical system until the drain has been isolated. Repair shorts or replace components as required.

A DRAIN ON FUSE 25

Fuse 25 supplies power to several of the interior lights, the center console light in particular. The center console light is activated by unlatching the center console armrest. If the armrest is not fully lowered and relatched, this light may remain illuminated.

On the 1987 Allante, power is provided to terminal B of this lamp "at all times" by circuit 440, a red and white wire. On the 1988 Allante, however, this lamp is wired into the Retained Accessory

Power (RAP) circuit. This prevents the light from remaining on for extended periods due to an unlatched console armrest.

On 1987 Allantes exhibiting an excessive battery drain condition on fuse 25, the center console lamp should be wired into the RAP circuit. Use the following procedure. Refer to pages 8A-114-2 and 8A-134-0 of the 1987-1988 Allante Service Information Manual.

1. Disconnect the negative battery cable.

2. Back out circuit 440 from cavity B of the center console lamp connector.

3. Tape this wire back to the console harness to prevent rattling and shorts to ground.

4. Back out circuit 142, a red and black wire, from cavity B of the trunk lid release switch connector (also on console).

5. Take a 4 inch length of 18 AWG (.8 metric) wire and connect a terminal (that will insert into the console lamp connector) to one end.

6. Solder the other end of the wire to the top of the terminal at the end of circuit 142.

7. Re-insert circuit 142 into cavity B of the trunk lid release switch connector.

8. Insert the terminal at the other end of the jumper wire into cavity B of the center console lamp connector.

9. Reconnect the negative battery cable.

DRAIN ON CIRCUIT BREAKER 24

Circuit breaker 24 supplies power to the soft top pulldown motor. It is possible for a misadjusted soft top or soft top pulldown motor to allow the pulldown motor to operate continuously. This may not be seen or heard during an inspection of the vehicle.

If the excessive drain on the battery is eliminated when circuit breaker 24 is removed, the soft top and/or soft top pulldown unit may be misadjusted, causing the motor to continuously operate. The motor will feel warm upon inspection.

Refer to Serviceman Bulletin T-88-64, Group 10 for soft top and soft top pulldown motor adjustment procedures.

DRAIN ON FUSE 8

Fuse 8 supplies power to the central power supply (CPS). The CPS, in turn, supplies power to the body computer module (BCM). A BCM remaining powered can cause a 700-950 mA drain on the battery.

The BCM may remain "awake" if it is receiving some type of "wake-up". Page 8A-50-4 of the Allante Service Information Manual provides a schematic of all of the possible BCM wake-ups. Most wake-ups are switches that toggle a BCM voltage to ground. Thus, the BCM could interpret a shorted wire or stuck switch as a legitimate wake-up and remain awake.

To determine if the BCM is receiving an erroneous wake-up, while the drain is present, enter BCM diagnostics and exercise all of the BCM inputs; B103 (LH door jamb switch), B104 (RH door jamb switch), B130 (time/temp display switch), B160 (theft alarm), B161 (door unlock switch), B192 (headlights). When an input does not alternate between Hi and Lo, there may be a problem with the associated switch or wiring that could cause the BCM to wake-up.

B161, the door unlock switch, should be checked first. If this switch remains grounded, or, if there is a short to ground on circuit 262, not only will there be a battery drain, but arming the theft deterrent will be impossible and the central door unlocking feature will not be fully operational.

If diagnosis identifies the door unlock switch circuit as remaining grounded, both the left-hand and right-hand switch circuits will have to be inspected. Inspection should include checking for chaffed or damaged wiring in the door panel as well as a damaged or sticking switch. Also be sure that the wires in the switch connector are in the correct cavities; circuit 262, a green and white wire, should be in cavity B and circuit 1503, a black wire, should be in cavity A.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.