Instruments - Oil Pressure Indicator & Gauge Information
Bulletin Number: 92-8-38Reference Number: 338302R
Publish Date: 3/93
Subject:
INFORMATION ON OIL PRESSURE INDICATOR LAMP AND GAUGE SERVICE
Models Affected:
1992 FIREBIRD MODELS WITH V-6, GRAND PRIX MODELS AND TRANS SPORT MODELS WITH 3.1L
During the 1992 model year, the above vehicles changed from an oil pressure "SENSOR" to an oil pressure "SWITCH". The switch, along with an inline resistor, is used to make the gauge operate as an indicator rather than a gauge.
Some confusion appears to exist on how to service these vehicles if the gauge or indicator becomes inoperative. The vehicles should be serviced by replacing the parts as they were built. In other words, if the vehicle was built with a sensor, replace it with a new sensor. If it was built with a switch, replace it with a switch.
The parts are located in Group 1.800 of the GMSPO catalog. A sensor (also called sender) is about 3-3/4" long. A switch is about 2-1/4" long. The sensor produces a variable resistance signal, and a switch produces an "open" or "closed" signal.
If a switch is installed instead of a sensor, the gauge will read "O" or "L" with the key on, then peg to the high side as soon as the engine is started. The switch is closed until it sees about 4 psi pressure, then opens, so the gauge sees this as an open circuit.
If a sensor is installed instead of a switch, the gauge will read "O" or "L" with the key on, then will stay very low with the engine running. The resistance of the sensor is added to the built-in resistance of the circuit, causing the total resistance to be lower than it should be, making the reading much lower than normal.
Service bulletin 92-8-30 issued 10/92 is a Service Manual update on the operation of the switch circuit in Grand Prix models.