Test Principles

BASIC CHECKS
It is important to carry out certain basic checks before starting fault-tracing. Cars with transient surge protection relay: Check that the 10-amp fuse on the transient surge protection relay is intact. Cars without transient surge protection relay: Check fuse (15 Amp) on fuse panel. 960: 11/22 Once the fuses have been checked, it is easier to carry out the other checks with the test box connected.

IGNITION ON
The voltage should be 0 volts on control module terminals 4, 9, 20, 21, 34. The voltage should be 5 volts between the control module ground and terminal 12. The voltage should be 12 volts between the control module ground and terminals 1 and 17.





CHECKING DTCs AFTER TAKING ACTION
If fault-tracing results in taking action, carry out a final check using the diagnostic system. All components must be installed and connected.
- Check that control module is connected.
- Erase DTCs.
- Start engine.
- Test drive car.
- Read off DTCs in DTM 1.
Once all faults have been dealt with, the only code left should be 1-1-1. If another DTC appears: Follow fault-tracing procedure for that DTC.





TEST POINTS AND SYMBOLS
Tests on connector: Connect control module to a 35-pin connector. The connector/control module connector pins are designated A1 to A35.

NOTE: Be careful when taking readings on connector pins.





Connectors fitted to other components have pins numbered 1, 2, 3 etc. Readings on such connectors must always follow a diagram showing pin numbers. Test box connections for test equipment which matches the control module connector are numbered #1, #2, #3 etc. as shown in the picture.





TEST EQUIPMENT
Fault-tracing involves using a voltmeter and ohmmeter (or a multimeter which can serve as both).

POWER SUPPLY
Measuring the voltage across terminal contacts can be done on the side of the connector, but is easier to do via the test box when connected. When taking voltage readings, connect the voltmeter to a ground point (O V) and the + test lead to the specified test point. When taking a number of voltage readings in succession, all you need do is move the test lead positive from one test point to another and leave the ground connection as it is. Where a voltage should be equal to the battery voltage, the variation should not be greater than approx. 0.5 volts. If it is greater, check for loose connections or oxidation.

NOTE: When measuring the voltage in a circuit, there will always be a voltage differential because switching on causes a certain current to flow in the circuit. This current varies with the load.





RESISTANCE READINGS
^ Resistance readings across a component are taken by connecting the test box without the control module.
^ Measuring lead resistance, on the other hand, usually involves disconnecting the lead connector from the component.

FAULTS IN LEADS OR COMPONENTS
^ If there is a suspicion that there is an open-circuit or short in a lead refer to the DTC fault-tracing sections.
^ Faults can of course also occur in individual components in the form of open-circuits, short-circuits or failure to work.

GROUND POINTS IN CAR CHASSIS
There are some points in the car which are reference points for O volts (ground points). There is always a certain potential difference (voltage difference) between them: this makes it important to use the right ground point, particularly when measuring analog signals.