Engine Controls - Lambda Control System Troubleshooting
87bmw10GROUP 13 Fuel System
Bulletin Number 13 03 87 (1351) Page 1 of 3
Montvale, NJ April 1987 Technical Dept.
SUBJECT: Troubleshooting of Lambda Control System
MODEL: All with Motronic M1.1
Symptoms: ^ "CHECK ENGINE" light illuminated during driving and 2-flash code display with ignition key in position 2.
^ Car may be hard to start and idles roughly.
Causes: ^ Fuel mixture too lean or too rich due to malfunctions of different engine components, which make the Lambda Control System exceed its programmed threshholds.
^ Failure of oxygen sensor and/or failure in oxygen sensor harness.
Condition: The M1.1 system with its self-diagnostic capabilities clearly differentiates between problems which make the Lambda Control System exceed its threshholds and those problems which are strictly related to the malfunction of the oxygen sensor.
The self-diagnosis makes this difference by using two different fault location code numbers.
With a 2-flash code indicated by the "CHECK ENGINE" light, the Fault Location display on the Service Tester screen will be as follows:
Fault Location 10 Oxygen Sensor* Means: Lambda Control System threshholds exceeded, problem not related to oxygen sensor itself and/or
Fault Location
28 Oxygen Sensor Means: Problem strictly related to Oxygen Sensor
or Oxygen Sensor Harness
* Defect description under Fault Location 10 will be changed to Lambda Control System with the next issue of the software.
Correction: With the Service Tester hooked up, troubleshoot as listed below and repair as necessary.
Troubleshooting
Procedure: 1. Connect Service Tester to engine and read out DME failure memory.
2a. If other than Fault Location 10 codes are displayed, repair according to the procedures of the Service Tester and the Electrical Troubleshooting Manual. Do not proceed any further.
b. If only Fault Location Code 10 is displayed, go to step 3.
c. If Fault Code 10 and other Fault Codes are displayed, repair these other Fault Codes first. Clear defect memory by pushing 999 on BMW Service Tester. Run engine undervarying load conditions. Proceed with step 3 only if Fault Code 10 is displayed again.
3. Check for air leaks (especially at secondary crankcase ventilation hose, idle valve hoses, rubber boot between airflow meter and throttle butterfly housing, gaskets between intake manifold and throttle butterfly housing and cylinder head) and correct as necessary. If obvious air leaks have been found and corrected, do not proceed further.
If no obvious air leaks have been found, proceed with step 4.
4. Check electrical (if not previously performed under step 2) and mechanical functions of charcoal filter purge valve:
a. Electrical Function: Refer to Electrical Troubleshooting Manual, page 1360A-01 and repair or replace as necessary.
b. Mechanical Function (valve might stick open):
- Detach hoses and plug from purge valve.
- Remove purge valve from engine.
- Attach vacuum pump hose of BMW Service Tester to 8 mm fitting of purge valve
- Supply 12 volts to purge valve being closed (do not reconnect original plug for voltage supply).
- Set BMW Service Tester to Multimeter Program 21.
- Switch on vacuum pump.
- Adjust vacuum pump of BMW Service Tester to 600 +/- 100 mbar.
- Let vacuum pump run for 10 seconds, then switch off vacuum pump, - After another 20 seconds, read the vacuum drop:
^ If the vacuum drop is smaller than 50 mbar, the purge valve does not have to be replaced.
^ If the vacuum drop is greater than 50 mbar, the purge valve has to be replaced.
- Install purge valve and connect plug and hoses properly.
If the purge valve was defective and had to be replaced or repaired, do not proceed any further.
If purge valve is okay, continue with step 5.
Note: The Control Unit shuts off the tank purge adaptation after every 7 minutes and goes back to the basic adaptation for 1 minute. During this one minute, the purge valve is closed and does not pulsate.
5. Read the defect description for Fault Code 10. If the reading is:
"Short to ground" . . . . . . . . . . . . . . . . . . . Go to step 6. "Short to battery" . . . . . . . . . . . . . . . . . . . Go to step 7.
6. Under Fault Code 10 "Short to ground" means the fuel mixture is too rich.
In the previous steps (1 to 5) most of the components that could influence the mixture as being too rich have already been checked or repaired.
Remaining items/functions to be checked additionally are:
^ Extremely diluted oil.
^ Fuel pressure regulator. Pull off the vacuum hose from the fuel pressure regulator. If you find fuel inside the hose, the diaphragm is leaking and the pressure regulator has to be replaced.
^ DME main relay.
^ Fuel pump relay.
^ Stuck open injectors.
7. Under Fault Code 10 "Short to battery" means the fuel mixture is too lean.
In the previous steps (1 to 5) most of the components that could influence the mixture as being too lean have already been checked or repaired.
Remaining items/functions to be additionally checked are:
^ Sealing of injector rubber rings at intake manifold.
^ Clogged injectors.
^ Insufficient fuel pressure (fuel pressure regulator, fuel pump, pinched fuel hoses, extremely clogged fuel filter.
^ Bad fuel (water in fuel).