July 2019 Service and Repair Manual
Manifolds
Part No. 1286829GT S-40 XC • S-45 XC • S-40 TraX • S-45 TraX 75
How to Test a Coil Diode
Properly functioning coil diodes protect the
electrical circuit by suppressing voltage spikes.
Voltage spikes naturally occur within a function
circuit following the interruption of electrical current
to a coil. Faulty diodes can fail to protect the
electrical system, resulting in a tripped circuit
breaker or component damage.
Electrocution/burn hazard.
Contact with electrically charged
circuits could result in death or
serious injury. Remove all rings,
watches and other jewelry.
1 Test the coil for resistance. Refer to Repair
Procedure, How to Test a Coil.
2 Connect a 10W resistor to the negative
terminal of a known good 9V DC battery.
Connect the other end of the resistor to a
terminal on the coil.
Note: The battery should read 9V DC or more when
measured across the terminals.
1 multimeter
2 9v DC battery
3 10Ω resistor
4 coil
Note: Dotted lines in illustration indicate a reversed
connection as specified in step 6.
3 Set a multimeter to read DC current.
Note: The multimeter, when set to read DC current,
should be capable of reading up to 800 mA.
4 Connect the negative lead to the other
terminal on the coil.
5 Momentarily connect the positive lead from
the multimeter to the positive terminal on the
9V DC battery. Note and record the current
reading.
6 At the battery or coil terminals, reverse the
connections. Note and record the current
reading.
Result: Both current readings are greater than
0 mA and are different by a minimum of 20%.
The coil is good.
7 Result: If one or both of the current readings
are 0 mA, or if the two current readings do not
differ by a minimum of 20%, the coil and/or its
internal diode are faulty and the coil should be
replaced.
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