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Starter Relay Circuit

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Severity

Medium

Can I keep driving?

Usually drivable, but get it diagnosed without delay.

First step

A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training. 1. Pull the relay out and physically check it, then swap it with an identical relay from the same fusebox (the wipers or horn relay is often the same part) and see if the fault moves or clears. This is the fastest, cheapest test and sorts a big chunk of P0615s on the spot 2.

  • PPowertrain
  • 0Generic code
  • 6Computer Output
  • 15Sequence number

What does it mean?

OBD II fault code P0615 is a generic code that is defined as “Starter motor relay -circuit malfunction”, and is set when the PCM (Powertrain Control Module) detects an abnormal voltage in any of the circuits that pertain to the starter motor relay. In terms of operation, the starter relay is a switch that closes a high-amperage circuit to supply battery voltage to the starter motor when it is activated with a low-amperage circuit.

The advantage of this approach is that the ignition switch does not have to cope with the extremely high amperages that some components, such as the starter motor, require to work efficiently. For a relay to work, it requires an input voltage, and in this case, the input voltage is supplied when the ignition key is turned to the “Start” position.

When the input circuit is completed, an electromagnet is activated, and battery voltage is passed through the contacts (which are kept closed by the magnet) directly to the starter motor solenoid, which in turn, activates the motor itself to crank the engine. When the ignition key is released, the input voltage is interrupted which de-energizes the electromagnet, thereby causing the spring-loaded contacts to return to the open position.

Depending on the application, the starter relay may have more than the usual four pins. On four-pin designs, one pin is for the input voltage, and one is to lead the input voltage back to battery negative, or ground. Of the two remaining pins, one is connected to the battery (usually through a fuse), while the other is connected to the component, in this case, the starter motor solenoid. On a five-pin design, one pin is usually used for a feedback signal to the PCM.

The image below shows a typical four-pin 12V relay, such as might be found in the starter circuit of many applications. Note however that on many modern applications, the relays are not electromechanical. Instead, relays are of the solid-state type in which electronic switches are used, thus eliminating all moving parts from the relay.

Symptoms

Likely causes

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This information follows the generic OBD-II definition and does not replace a vehicle-specific diagnosis. The severity rating is rule-based; an authorised diagnostic reading is required for a definitive answer.