DEAD BATTERY OR NO CRANK AFTER OVERNIGHT SET

Models Affected: All Vehicles 1980-84 Equipped with ECM

If a vehicle exhibits a low or dead battery after an overnight set, or goes down over a period of 2 or 3 days, the electrical system should be checked for an excessive electrical drain using the following procedures.

Remove the underhood lamp bulb (if equipped) and turn ignition off.

Charge the battery to a full state of charge.

If the vehicle is equipped with Electronic level/Ride control ELC, disconnect the exhaust valve connector at the pump (See Figure 1). Note: ELC exhaust valve must be disconnected before test because design of the exhaust valve will cause a .5 amp drain for 4-6 minutes after the ignition is turned off.

Disconnect negative battery cable, connect an ampmeter capable of carrying at least 20 amp in series between the battery terminal and the negative battery cable. With the key off note amperage draw (should not be more than 0.5 amp, doors closed all systems turned off).

If more than 0.5 amp drain is present the vehicle's electrical system should be checked by pulling fuses to determine component causing the excessive amperage drain.

If the larger capacity ampmeter indicates less than 0.5 amps remove it from the battery and install the digital volt ohm meter in its place. Set the left selector switch an the digital volt ohm meter to the MA scale, center slide switch to DC low volts, and the right selector switch to 2,000 scale.

NOTICE: Do not open doors or operate any equipment that would draw more than 2.0 amps or the fuse on the digital volt ohm meter will blow. If blown, it must be replaced with a 2 amp fast blow fuse only or meter will be damaged.

Starting with the 2,000 MA (milliamps) setting start switching the right selector switch down the scale until an accurate amperage drain reading is obtained.

Normal parasitic current drains on the battery are 10 MA (milliamps) to 30 MA (milliamps). If more that 30 MA drain is indicated on the digital volt ohm meter the vehicle's electrical system components such as ignition switch, twilight sentinel control, trunk lamps, tone generators etc. should be checked to determine the component causing excessive drain on the battery.

ECM TEST:

If during previous testing excessive amerage draw was found (over 30 MA) the ECM should be tested as follows.

Remove digital volt ohm meter, reconnect battery cable to battery.

Connect the ALDL scan tool to the ECM ALDL diagnostic connector under the instrument panel.

Turn ignition switch on for 5 seconds and then off. With ignition off the ALDL scan tool should read "NO ALDL".

If data is still being displayed on the AIDL scan tool and the ignition has been off for at least 10 seconds the ECM is staying powered up when it shouldn't be and should be replaced. If the ECM is replaced the same on-off test should be performed again to insure the problem is corrected.

NOTE: Any ECM found with this failure mode should have the failure noted on the yellow ECM return tag as "Battery goes dead ECM stays powered up with ignition off".

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.