On- Vehicle Testing

Fig. 1 Alternator Output Test. Bosch 55 Amp Alternator w/Integral Regulator:

Fig. 2 Alternator Output Test. Bosch 70 Amp Alternator w/Integral Regulator:

***UPDATED BY TSB 32107, MARCH 1986
When testing an alternator, it is important that a fully charged battery be used.

BOSCH ALTERNATOR W/INTEGRAL REGULATOR

Alternator Output Test

1. With alternator at normal operating temperature, run engine at 3000 RPM for 3 minutes.
2. Using a suitable shunt or loading alternator with accessories to require 40 amps, check output and compare to Fig. 1 for 55 amp alternator or Fig. 2 for 70 amp alternator.
3. If alternator does not produce current within specifications, check brushes. If brushes are satisfactory, repeat test using a known good regulator. Indicator on dash must not glow during any part of the testing procedure, if so one or more diodes are defective. Also maximum voltage difference between B+ and D+/61 is 1/2 volt.

Voltage Regulator Test

1. Run alternator until normal operating temperature is reached.
2. With the engine running at 3000 RPM, measure the voltage between B+ and D- terminals on back of alternator.
3. Correct reading should be 13.4-14.2 volts. If voltage is incorrect, make sure alternator brush length is correct. Minimum brush length is .2 in. (5 mm). If brush length is satisfactory, replace regulator.

Temperature Sensor Test

Some 1985-87 model vehicles use an external temperature sensor located underneath the battery. This sensor, directly connected to the voltage regulator, senses battery temperature and relays this information to the regulator. During cold weather operation, the alternator delivers higher voltage to the battery, thereby charging it at a faster rate. As the battery warms, the charging rate is reduced to prevent excessive gassing. To check sensor operation, proceed as follows:

1. Note and record battery temperature.
2. Connect voltmeter across battery terminals, then with all accessories off, start engine and allow to run at 2000 RPM. Observe charging voltage.

Fig. 3 Charging Voltage Graph (w/external Temperature Sensor Connected):

3. With battery temperature as noted in step 1, charging voltage should be within shaded areas of graph, Fig. 3. If voltage is as specified, temperature sensor is functioning properly. If not, proceed to next step.

Fig. 4 Charging voltage graph (w/external temperature sensor disconnected):

4. Disconnect external temperature sensor from regulator, then repeat steps 1 and 2. With battery temperature as noted, charging voltage should be within shaded areas of graph, Fig. 4. If voltage is as specified, replace temperature sensor. If voltage is not as specified, replace voltage regulator.