A P0818 trouble code is related to a four wheel drive vehicle’s transfer case and its neutral position switch (driveline disconnect).
What the P0818 code means
P0818 is an OBD-II generic code for a voltage problem with a four wheel drive vehicle’s transfer case neutral position switch. If the engine computer detects a signal from the switch indicating the transfer case is in neutral when the vehicle is in high range or moving, it will indicate a problem with the switch itself, causing a P0818.
What causes the P0818 code?
The most common causes for a P0818 are:
- Faulty transfer case indicator switch wiring harness and or connector
- Faulty neutral position switch
- Faulty wiring or ground from transfer case switch to engine computer
- Faulty engine computer
What are the symptoms of the P0818 code?
Because a P0818 indicates the transfer case is in neutral when it in fact is not, there should be no noticeable symptoms other than a check engine light. If you encounter this code, it’s wise to ensure your transfer case will shift from high range, neutral, and low range.
How does a mechanic diagnose the P0818 code?
It’s likely your mechanic will first clear the code, reset the engine computer, ensure the transfer case is in a normal position, and test drive to ensure the P0818 comes back. If it does, they will then move on to the switch connector and wiring harness, testing both for proper resistance. If either do not meet the manufacturer’s specifications, they should be replaced. If they do however, there could be an issue with the neutral position switch itself. This should be tested for resistance and replaced as necessary.
While rare, a bad ground or connector between the engine computer and the transfer case wiring harness could cause a P0818, but this won’t be investigated until it’s confirmed both the neutral position switch and wiring harness are in good condition.
Common mistakes when diagnosing the P0818 code
Driver error may cause a P0818 to become a stored code, so it’s wise to first clear the code, reset the ECU, and test drive the vehicle before parts are replaced.
How serious is the P0818 code?
A P0818 by itself shouldn’t cause any mechanical or driveability issues. However, if it is accompanied by other codes, there could be an issue with the transfer case wiring.
What repairs can fix the P0818 code?
The most common repairs for a P0818 are as follows:
- Replacing the transfer case neutral position switch
- Replacing damaged wiring and or connectors for the neutral position switch
- Cleaning bad grounds for the neutral position switch
While rare, replacing the engine computer may be a needed repair as well.
Additional comments for consideration regarding the P0818 code
P0818 codes are common in Toyota SUVs and 4x4s - especially FJ Cruisers and Lexus LX/GX models.
Need help with a P0818 code?
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This article originally appeared on YourMechanic.com as P0818 OBD-II Trouble Code: Driveline Disconnect Switch Input Circuit and was authored by Logan Utsman.