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P0817 OBD-II Trouble Code: Starter Disable Circuit

diagnostic check engine light

P0817 code definition

The starter disable circuit is also referred to sometimes as “ignition interlock” or “neutral safety switch.” Its function is to interrupt the current to the starter if the transmission is in gear and not in “PARK” or “NEUTRAL,” or if the clutch is not disengaged on a manual transmission. The P0817 code is registered when the powertrain control module (PCM) detects a level of current that is not in line with factory specs. A code is then stored and the malfunction indicator lamp (MIL) is illuminated.

What the P0817 code means

A P0817 code denotes a fault in the circuit that prevents the vehicle from being started while in gear.

What causes the P0817 code?

Causes commonly include:

  • Starter disable relay failure
  • Blown fuse
  • Starter relay failure
  • Starter motor or solenoid failure
  • Failed battery cable or cable ends/clamps
  • Shorted or open circuits

What are the symptoms of the P0817 code?

Symptoms of the P0817 code usually are an illuminated MIL light, a no start condition, or a no crank condition.

How does a mechanic diagnose the P0817 code?

Some vehicles have the starter connected directly to the battery and ignition switch. The heavy-gauge battery cable is connected directly to the starter solenoid with an eyelet-style cable end that goes directly onto the solenoid’s stud, and is secured with a nut and washer. This design is often called a primary circuit.

Other vehicles use a starter relay which is connected to the battery cable and ignition switch. When the ignition key is turned, the starter relay is activated and causes the starter solenoid’s contacts to close. When the solenoid contacts close, battery current goes to the starter motor, causing it to engage the flywheel and turn the engine over.

  • Begin the diagnosis by visually inspecting the battery cables and cable ends. Clean/replace cables and ends as needed.
  • Make sure the battery is fully charged. Perform a load and starting/charging test on the battery. Compare your findings with factory specs and replace any failed components as needed.
  • If the battery and charging system check as normal, start tracking down the systems’ fuses and fusible links and test.
  • Visually inspect all wiring and circuit, and replace any failed components as needed.
  • If all fuses, fusible links and wiring check out as OK, test the starter end of the battery cable for voltage. Use a digital volt/ohmmeter (DVOM) and check the cable as the ignition switch key is turned to the “start” position.
  • If the voltage drops when the ignition switch key is turned to “start,” suspect a problem with the battery cable or battery cable connection.
  • Check the starter’s ground connection, remembering that the starter is grounded by its own mounting bolts that attach it to the engine block.
  • If the vehicle uses a starter relay as a secondary circuit, place the DVOM’s voltage end on the starter solenoid. Locate the small stud and retaining nut at the rear of the solenoid, opposite the battery cable stud, and place your DVOM probe there. Have an assistant toggle the ignition switch from “start” to “run,” repeatedly.
  • The secondary circuit should only have battery voltage with the ignition switch in the start position.
  • If no voltage is present on the secondary wire, move on to the starter relay. Test the starter relay’s input circuit and compare to factory spec.
  • If input readings are in line with factory specs but there is no output voltage signal, replace the starter disable relay. If no ignition switch input signal shows up at the starter disable relay, suspect the ignition switch. NOTE: this refers to the electrical portion and not the cylinder.
  • If other input signals fail to agree with factory specs, disconnect the relay connector. Perform a continuity test between the connector and fuse panel. Repair any open or shorted circuits and retest.
  • Test the PCM’s input signal from the starter relay and repair/replace any shorted or open wiring.
  • If the PCM input signal is present, suspect a failed PCM but remember that PCM failure is rare.

Common mistakes when diagnosing the P0817 code

Newer vehicles have more problems with the starter motor’s voltage supply and relay than the motor itself, but often a snap diagnosis will lead a technician to replace the starter itself unnecessarily.

How serious is the P0817 code?

A P0817 code can result in a no start/no crank condition.

What repairs can fix the P0817 code?

Additional comments for consideration regarding the P0817 code

As with many other repairs, a P0817 code can be the result of a few different problems. Careful, patient step-by-step process of elimination is essential to properly troubleshooting and repairing this problem. Also note that code setting parameters can vary from one make to another, and many applications will require multiple failure cycles with a P0817 code before the MIL will be illuminated and a hard trouble code stored in the PCM. This article is only a general set of guidelines, as the design of the starter/ignition circuitry can vary greatly from one make to another.

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