Electrical - Ground Test By Voltage Drop

NO.
909

GROUP
37

SECTION
3

DATE
May 1994

RE:
Measurement of voltage drop across ground connections

All 700/900 series

REFERENCE:
TP 31465/1 SECTION 3(31-33) BATTERY, ALTERNATOR, STARTER MOTOR, 200/7W 1975-19..

Measurement of voltage drop across ground connections

When tracing a wiring fault suspected to be due to a poor ground connection, the ground terminal should be checked as described below.

CAUTION!
The voltage drop must not be measured across any SRS ground terminals since these leads are not normally live. No service other than that described in the SRS service manual may be carried out on this system.





Test equipment:
FLUKE 88 or equivalent test instrument

Method of checking ground terminal:

Start engine and operate following functions during measurement:
High beam, blower (at maximum speed), seat heaters, rear window heater and A/C.

Connect test probes as illustrated and read instrument. Complete cable terminal, including conductor strands, should be included in measurement. It is important that test probe tips should be sharp to ensure good contact.





If conductor strands are not accessible, probe should be placed at point (A) in illustration.

Permissible voltage drop

Max. permissible voltage drop at signal and power ground terminals (31/33 and 31/32) connected to fuel injection system is 5 mV (0.005 V).

- Max. permissible voltage drop at other ground terminals, such as
- battery to body
- battery to engine is 20 mV (0.020 V).

High voltage drop may be due to poor crimping, dirt or oxidation. It is important to measure between conductor strands before crimped joint and support/boss immediately adjacent to terminal to detect poorly crimped connection or oxidation.

If voltage drop is too high, undo terminal screw and clean oxidation and dirt from terminal point and cable terminal with emery cloth. Check that cable terminal is intact and that lead is firmly seated in it.

Reconnect lead using new terminal screw.

Note!
Serrated washers should not be used in terminal connections since these may increase contact resistance.

Ground terminal screw torques:
Engine (not diesels) 949845-2 M6*20 10 N-m, 7.5 ft.lbs
Windshield wipers 979780-4 M6*12 10 N-m, 7.5 ft.lbs
Body 979781-2 M6*16 10 N-m, 7.5 ft.lbs
Other M8 20 N-m, 15 ft.lbs
Other M10 40 N-m, 30 ft.lbs

Repeat measurement to ensure that value is within specified limit.

When value is correct, treat terminal with anti-rust agent, P/N 1161435-1.





Example of engine ground terminal, B6304

Power ground: SB or BL lead
Signal ground: BN lead





Example of engine ground terminal, B230





Example of body ground terminal