P2503 – Charging system – voltage low

Stephen Darby

By Stephen Darby (Contact Me)
Last Updated 2022-05-13
ASE Master Tech

CodeFault LocationProbable Cause
P2503 Charging system - voltage low
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Wiring, alternator, battery

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What Does Code P2503 Mean?

About a week ago, I was surprised when a service engine soon (SES) indicator was illuminated in the instrument cluster of my daily driver. The amber colored SES lamp was accompanied by a bright red battery lamp. Before I could address the issue, my vehicle failed to start due to insufficient battery voltage. I was perplexed.

After having the SUV towed home, I used one of my code readers to access trouble code data. The code stored in the powertrain control module (PCM) was a P2503 – Charging System Voltage Low. A stored code P2503 indicates that the PCM has detected a level of system voltage that is inadequate to maintain vehicle operation. The cause of this type of code may be an electrical (wiring/connector) issue or a mechanical (component failure) issue.

Prior to clearing stored codes from the PCM, I logged the pertinent data on a note pad for future reference. This included freeze frame data and all stored codes. This information would prove helpful as diagnosis of the P2503 unfolded.

My diagnosis began the following morning with the vehicle cold and the battery freshly charged using a suitable battery charger. Again, I was surprised to discover, when I started the engine, the SES lamp was not illuminated, nor was the red low battery indicator. With the engine running, I connected my digital volt/ohmmeter (DVOM) to the appropriate terminals of the battery and observed charging system voltage. Typically, charging system voltage should be between 12.9 and 13.8 volts with the engine running. My charging system voltage was within specifications and the P2503 had not been reset. This was a disturbing development.

I left the vehicle at idle and went about handling another small piece of business. When I returned to my diagnosis, I found the SES illuminated (along with the low battery lamp) and I reconnected my DVOM to the battery. I discovered that charging system voltage was not within the acceptable parameters and it was inadequate to maintain safe vehicle operation. Previously collected freeze frame data indicated that the original malfunction had occurred when engine temperature was approximately 210-degrees. Experience told me that internal alternator components frequently perform under cold start conditions and fail when hot.

Taking nothing for granted, I continued my diagnosis by testing charging system voltage directly at the alternator (using the DVOM). I found that alternator output voltage was insufficient. After testing all alternator input circuits – and the ground – I concluded that the alternator was defective.

With the new alternator installed, I cleared the codes and test drove the vehicle. Problem solved.

What are the common causes of code P2503?

Other causes of a stored code P2503 could include a blown fuse, fusible link or circuit breaker. This is often caused by incorrect jumper cable use. If I had discovered insufficient input voltage at the alternator, I would have proceeded to test all charging system related fuses, circuit breakers and fusible links. Consult the vehicle service manual for fuse locations.

Some other likely causes of a stored code P2503 may include a bad battery, loose/corroded battery cable ends or even a defective PCM. Several automakers use a voltage regulator that is integrated into the PCM.

Codes Related to P2503

P0562 applies to battery voltage and may be stored with KOEO.  P2503 only pertains to a KOER condition when the charging system is operational.