Checking Diodes and Vehicle Electrical Systems

What is a diode?

Near the alternator, the electric generator of the vehicle, you will see another piece of equipment, a diode. Diodes within vehicle applications are striped cylindrical components, that ensure current flows in a single direction. The diode is often just as important as any other vehicle component, protecting other vehicle equipment from current spikes, which may damage components and the electrical system as a whole. This causes the vehicle to stop working, preventing customers from getting where they need to be, on time.

Typically, there are approximately six diodes connecting the alternator with the battery and the electrical system, converting alternating current into direct current. Alternating current can switch directions, whereas direct current is a consistent flow of electricity. Direct current is needed for battery and vehicle operation, as it provides higher efficiency at a lower cost.

Identifying diode issues

Vehicle non-starts and power-related problems often make a customer think there is an issue with the battery, but this is not always the case. When diagnosing a vehicle problem, it is just as important to check the electrical system as a whole is functioning correctly, or battery replacements may not fix the problem, and could just become an additional and unnecessary expense. Problems with keyless entry, remote start, or start/stop systems, can often be traced back to issues with the vehicle diode, instead of the battery.

Diode problems also manifest as a battery that fails to charge correctly or a noise within the electrical system. This is as the diode fails to convert alternating current into direct current, which disrupts electronics. A diode that has shorted allows an excessive amount of drainage, and discharges a battery quickly, due to current issues.

To find a diode issue, you can use a battery and electrical system tester, which uses a ripple test to identify discrepancies. We recommend the Midtronics DSS-5000 for this application as it includes a ripple testing capability. If you don’t have access to this equipment, the alternator must be taken apart to test every diode independently.

Next steps

To ensure battery and electrical system issues are diagnosed correctly, we recommend diode tests are included within services, to reduce unnecessary costs and downtime for customers who may have to return if the problem is not identified the first time. This can also reduce company reputations, due to an incorrect diagnosis.

For more information, call 0121 514 0605.


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