Dynamic Oil Pressure System - Troubleshooting Tips
Group: 17Number: 92-03
Date: September 30, 1992
Subject:
Dynamic oil pressure system, general troubleshooting tips
Model(s):
All Except V8
M.Y. 1984-1992
Note:
This Bulletin gives an overview of system operation and general guidelines for troubleshooting the dynamic oil pressure system. For detailed troubleshooting information refer to the Repair Manual Microfiche. For Audi 4000's with 4-cylinder engines, 1984-1987, refer to Technical Bulletin Group 17, 90-04.
Condition:
Engine oil pressure light on.
System overview:
The dynamic oil pressure system consists of the following components:
^ oil pressure control module
^ oil pressure warning light
^ low pressure switch
^ high pressure switch
Oil pressure control module
The oil pressure control module operates the oil pressure warning light and buzzer/chime. In vehicles with the autocheck system, the oil pressure control module is integrated into the autocheck control module. In vehicles without the autocheck system, the oil pressure control module is a relay located in the auxiliary relay panel. In either case, the system function is the same.
^ below 2000 RPM, only the low pressure switch is used to determine low oil pressure. If the control module receives a ground signal from the low pressure switch, the oil pressure light will turn on. For vehicles with an autocheck system: a chime will sound three times. For vehicles without an autocheck system: no audible warning will sound.
^ above 2000 RPM, the high pressure switch is used to determine low oil pressure. The oil light will turn on if the control module loses the ground signal from the high pressure switch. For vehicles with an autocheck system: a chime will sound three times. For vehicles without an autocheck system: a buzzer will sound for as long as the light is on.
Oil pressure warning light
In vehicles with the autocheck system, the oil pressure light is included in the autocheck display. In vehicles without the autocheck system, the oil pressure light is located in the instrument cluster.
Low pressure switch
When the oil pressure is too low (below 0.3 bar), the low pressure switch closes and sends a ground signal to the oil pressure control module. When the oil pressure is above 0.3 bar, the switch is open.
High pressure switch
The high pressure switch works the opposite of the low pressure switch. When the oil pressure is sufficient (above the switch specification, see below), the switch closes and sends a ground signal to the oil pressure control module. When the oil pressure is too low (below the switch specification), the switch opens to ground.
High pressure switch open below:
^ 1.8 bar on 4 and 5 cylinder engines
^ 2.5 bar on V6 engines
Troubleshooting tips
Follow these guidelines when troubleshooting a dynamic oil pressure system:
1. What is the specific customer complaint?
^ Does the light come on above or below 2000 RPM?
^ How often does the light come on?
^ How long does it stay on?
^ What are the driving conditions when the light is on?
^ What value is displayed on the oil pressure gauge when the light is on (if so equipped)?
^ Can the complaint be duplicated?
2. Check oil level.
3. Check oil quality. (Is there sludge, contamination or dilution that could affect oil pressure?)
4. Check oil pressure with an external gauge at idle and above 2000 RPM. It may be necessary to check oil pressure at both switches if one is located on the cylinder head. DON'T ASSUME THAT THE OIL PRESSURE IS OK. If the vehicle has an auxiliary gauge and it shows sufficient pressure when the oil pressure light is on, don't assume that the gauge is reading correctly and that the dynamic oil system is malfunctioning.
5. Check for proper operation of the dynamic oil pressure system.
^ engine running less than 2000 RPM with wire to .3 bar oil pressure switch disconnected and grounded
^ oil pressure light must flash
^ buzzer/chime must NOT sound on vehicles w/o autocheck, must sound on vehicles w/autocheck
^ engine running greater than 2000 RPM with wire to the 1.8 or 2.5 bar oil pressure switch disconnected, but not grounded
^ oil pressure light must flash
^ buzzer/chime must sound
Potential problems to look for
1. Low oil pressure due to:
^ Low oil level
^ Diluted or contaminated oil
^ Defective oil pump or pressure relief valve
^ Mechanical engine problems
2. Incorrect low oil pressure signal from either oil pressure switch (oil pressure OK).
3. Low pressure switch circuit has short to ground (light on below 2000 RPM, oil pressure OK).
4. High pressure switch circuit has open circuit (light on over 2000 RPM, oil pressure OK).
5. Incorrect low oil pressure indication from oil pressure control module (oil pressure OK, no low oil pressure signals from oil pressure switches).