P0626 – Generator field terminal -circuit high

By Reinier (Contact Me)
Last Updated 2018-02-07
Automobile Repair Shop Owner

Table of Contents

1. What Does Code P0626 Mean?
2. Where is the P0626 sensor located?
3. What are the common causes of code P0626 ?
4. Get Help with P0626

What Does Code P0626 Mean?

OBD II fault code P0626 is a generic code that is defined as “Generator field terminal -circuit high”, and is set when the PCM (Powertrain Control Module) detects an abnormally high voltage in the generator field coil and its associated control circuit(s).

NOTE: Note that in recent years, the word “generator” has become synonymous with “alternator”.

Also known as the “stator”, the field coil in an alternator is the most easily identifiable component in almost any alternator, due to the copper wire windings that are almost always visible through the alternator casing. This part of the alternator remains stationary; the rotor rotates inside this part, and the interaction between the electromagnetic fields of the field coils and the rotor is what creates an alternating current when the rotor rotates inside the field coils.

In the context of code P0626, “field current” refers to the current within the field coils only, and NOT to any current or general power supply in the rest of the application’s electrical system. In practice, the current within the field coils has two sources; from the battery when the alternator is not rotating, and from the diodes in the bridge rectifier when the alternator is rotating fast enough to create a current.

In terms of operation though, the filed coils are supplied with current from the battery through the ignition switch and the charging system warning light when the ignition is switched on. When the engine starts and the alternator starts to spin, the current it generates is fed to the voltage regulator through the rectifier (which converts the AC current to DC), and from there it serves as the power supply for the field coils. At this point, the alternator is said to be self-sustaining, in the sense that the field coils no longer need to draw current from the battery. At this point, the charging system warning light is extinguished as an indicator that the alternator is generating sufficient current to meet the power demands of the application’s electrical consumers.

In a fully functional alternator, the voltage regulator maintains the current being generated in a range of between 13 and 14 volts, but on some applications, this can be as high as 15 – 16 volts. Nonetheless, since the current in the field coils derives from the voltage regulator when the alternator is spinning, a malfunctioning voltage regulator, and by extension, defective diodes in the rectifier, can cause the voltage in the field coils to spike to above maximum allowable levels for that particular application.

Thus, when the PCM (or other control module, such as a dedicated alternator control module) detects an abnormally high voltage in the field coils, it will set code P0626. Note though that whether or not a warning light is illuminated on the first failure depends on both the application, and the nature/severity of the problem.

Where is the P0626 sensor located?

The image below shows an exploded view of the principal components of a typical modern alternator. Note that the part labelled “Stator” is a metal ring that holds copper windings in place; the field coils are the sets of copper wire windings that protrude from both sides of the stator, or metal ring.

What are the common causes of code P0626 ?

Some common causes of code P0626 could include the following-

• Defective voltage regulator
• Defective rectifier
• Damaged, burnt, shorted, or corroded wiring and/or connectors in the field coil control circuit, but note that damaged wiring almost anywhere in the CAN (Controller Area Network) bus system can also cause this code, or contribute to its setting
• Poor contact between the battery negative terminal and post. On most applications, this could cause the alternator’s output, and hence, the current in the field coils to spike
• Failed or failing PCM or other control module. Note that these are rare events, and the fault must therefore be sought elsewhere before any control module is replaced

NOTE #1: If blown fuses or fusible links are found when diagnosing this code, it is important to establish the relationship between the charging system and circuit in which the blown fuses are located, and NOT to replace any blown fuses until the short circuit is found and repaired. In cases where the circuit containing blown fuses is related to the charging system, replacing blown fuses without repairing the short circuit could cause extensive damage to the application’s electrical system.

NOTE #2: In cases where the fuses or fusible links that protect the alternator directly is found to be blown, do NOT replace the blown fuses/fusible links until the alternator had been tested professionally, and especially on applications where the alternator’s output is controlled by the PCM. Replacing blown fuses/fusible links on these applications without having the alternator tested professionally could destroy one or more control modules, including the PCM.

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