OIL PRESSURE GAUGE MALFUNCTION DIAGNOSIS INFORMATION

VEHICLES AFFECTED: 1986 Toronado

Early production Toronado's are equipped with a three terminal oil pressure switch part number 25036925 instead of a four terminal sensor. During normal operation, the oil pressure will be at mid range on the gauge. When the body computer senses a mid range voltage between 0 and 5 volts instead of 0 volts (engine not running) or 5 volts (engine running) in the oil gauge circuit, the EEPROM is automatically reprogrammed to operate with a sensor.

The oil pressure sensor is not presently available, therefore after the malfunction in the oil pressure circuit has been corrected, access 'BCM DATA' and observe oil pressure (BD 71). If the pressure indicates 0 (engine not running) and 45 (engine running), clear the malfunction code and no further repairs are required.

If the pressure indicates 255 after making sure the oil switch connector terminals are clean and/or the oil pressure switch has been replaced, it will be necessary to replace the EEPROM as instructed in Product Service Bulletin No. 86-8-120

The diagnosis charts for codes B131 and/or B132 have been revised. Please update pages 8D2-30 and 8D2-31 of your 1986 Oldsmobile New Product Service Information Manual - Toronado with this revised information.

CODE B131 AND/OR B132 ENGINE OIL PRESSURE CIRCUIT PROBLEM

The oil pressure indicator uses a variable resistor or switch to control the signal voltage to the BCM. The BCM supplies a voltage on CKT 313 to the sensor. When the engine is not running (low oil pressure) the sensor's resistance is Lo, or switch closed to ground and the signal voltage is pulled Lo through sensor ground, CKT 736, or the engine block with a switch. When the engine is running (increased oil pressure) the sensors resistance becomes greater and the signal voltage increases or the switch opens, therefore the BCM will see a Hi signal voltage (open CKT). This signal voltage will vary between 5V (open CKT) and OV (shorted CKT).

Code B131 will set with key "ON" engine not running if the signal voltage indicates greater than 8 psi (open CKT). Code B132 will set if the engine is running and the signal voltage indicates greater than 80 psi (open CKT).

1. BCM data value BD71 displays oil pressure. The normal range is from 0 to 80 PSI. A value above 80 indicates an open or shorted to voltage circuit or sensor.

2. Checks to see if the open circuit reading is due to the circuit or sensor. If the open circuit reading changes to a shorted circuit reading after jumpering the senosr terminals, the BCM and wiring are OK.

3. By applying a ground to various points in the circuits, an open can be isolated by observing whether the parameter display can be changed from the open reading to the shorted reading.

Note on Intermittents

If an intermittent code B131 and/or B132 is being set, manipulate the related wiring while observing BCM data parameter BD71. If the failure is induced the reading will jump from 0 to some oil pressure with the engine 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.