Starter Disable Circuit
The PCM has detected an abnormal voltage reading from the starter disable circuit.
Code Set Parameters
Vehicles which utilize a starter relay to activate and engage the starter motor, require a battery voltage signal, ground signal, and an ignition switch input signal in order to operate properly. An output signal is also used to supply the PCM with data. The starter disable circuit is used to interrupt the voltage supply to the starter if the transmission is not in either “PARK” or “NEUTRAL” or if the clutch is not depresses on vehicles with manual transmissions. If the PCM detects a level of voltage that is not consistent with the manufacturer’s recommended specifications, a code will be stored and a malfunction indicator lamp will be illuminated. Some applications require multiple ignition cycles (with a failure) in order for the malfunction indicator lamp to be illuminated and others will activate the malfunction indicator lamp on the first failure.
Symptoms may range from just the service engine soon lamp and a stored code to a no start/no crank condition.
In choosing a single most common cause, I would have to say a faulty starter disable relay. Other common causes may include a blown fuse, a bad starter relay, shorted or open circuits, a defective battery, faulty battery cables/cable ends, or a defective starter motor/solenoid.
Snap diagnosis’ often lead to unnecessary starter motor replacement. Technicians report that shortcomings in the voltage supply to the starter motor are more common in late model vehicles than bad starter motors/solenoids.
- Some vehicles use a starter relay in order to activate and engage the starter motor with the flywheel
- Others use a system that does not include a relay but instead uses a wire that comes directly from the ignition switch
- The starter disable system is used sparingly by a handful of automobile makers
The opposite end of the positive battery cable (from the battery post) is typically attached to the starter solenoid using an eyelet style cable end placed over a solenoid integrated stud, with a nut threaded on to secure it
- The positive battery cable is often referred to as a primary circuit
- A separate wire from the starter relay, or directly from the ignition switch, is used to activate the starter solenoid and engage the starter motor with the flywheel
- This wire is sometimes called a secondary circuit
Of course, the supply of voltage on the positive battery cable should be constant
- The ignition switch (not the cylinder but the electrical switch which the cylinder engages) is used to activate the secondary circuit (in this case, via the starter relay) which causes the contacts of the starter solenoid to close
- With the solenoid contacts closed, battery voltage is supplied to the starter motor, causing it to spin and engage the engine flywheel, thus cranking the engine.
Begin your diagnosis with a visual inspection of the battery cables and battery cable ends
- Clean or replace cables and ends as required
- Make sure that the battery is fully charged and then perform a battery load and starting/charging system test
- Compare your findings with manufacturer’s recommendations and replace faulty components as needed
If the battery and starting/charging system are normal, then test system fuses and fusible links
- Replace faulty components as needed and retest the system.
Visually inspect all wiring and connectors
- Look for shorted or burned wiring and replace circuitry and connectors as required
- Most applications will require replacement of the full internal transmission harness if discrepancies are noted there
If the system wiring, connectors, and components appear to be in normal working order, connect the scanner to the diagnostic connector and record all stored trouble codes and freeze frame data
- This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
- After the codes are cleared, operate the vehicle to see if the code returns
- If the code fails to immediately return, you may have an intermittent condition
- Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made
If the problem persists, test the starter end of the battery cable for battery voltage
- Use a test light or digital volt/ohmmeter to check the starter end of the battery cable while the ignition switch key is turned to the “start” position
- A constant supply of battery voltage should be present
- If there is no voltage, or if voltage is diminished when the ignition switch is placed in the start position, suspect a faulty battery cable or battery cable connection
- The starter uses its mounting bolts to ground itself to the engine block
- Make sure that the battery ground cable is securely attached to the engine block by testing the engine block ground and starter housing ground
- If the starter motor housing has no ground, repair the ground cable or connection as required
- Next, place the voltage end of your testing device on the secondary circuit of the starter solenoid (the small stud and retaining nut opposite the battery cable stud on the rear of the solenoid) and have a helper rotate the ignition switch from the “start” to the “run” position, repeatedly
- The secondary circuit should have battery voltage with the ignition switch in the start position, only
- If there is no voltage on the secondary wire, move your testing to focus on the starter relay.
Test the input circuits of the starter relay and compare your findings with the manufacturer’s specifications
- If the input readings coincide with manufacturer’s specs, and there is no output voltage signal, replace the starter disable relay.
If there is no ignition switch input signal at the starter disable relay, suspect a faulty ignition switch (not the cylinder, the electrical portion)
If other input signals fail to line-up with manufacturer’s specifications, disconnect the relay connector and perform a continuity test between the connector and the fuse panel
- Repair open or shorted circuits as required and retest
- Test the PCM input signal from the starter relay and repair open or shorted wiring as necessary
- If the PCM input signal is present, suspect a faulty PCM (PCM failure is rare)