What Does P1818 Mean?
The neutral safety switch circuit has a short to battery voltage, providing constant power when it should be a switched ground signal. This prevents the PCM from properly determining if the transmission is in Park or Neutral for starting safety interlock.
Safety Warning
Vehicle may start in gear, creating serious injury risk. Vehicle may not start at all if PCM detects fault and disables starter circuit.
Common Causes
40%
Damaged wiring harness with neutral safety switch wire shorted to power source
30%
Failed neutral safety switch with internal short to power circuit
20%
Corroded or damaged connector with cross-circuit contamination
10%
Aftermarket accessory installation causing wiring damage or improper connections
Diagnostic Steps
1
Step 1: Disconnect neutral safety switch connector and measure voltage on switch circuit wire toward PCM (should read 0V)
2
Step 2: Inspect harness for damage, particularly where it routes near starter motor, battery cables, or alternator
3
Step 3: Check switch connector for corrosion, melted plastic, or damaged pins causing shorts
4
Step 4: With connector still disconnected, move transmission through all gear positions while monitoring circuit voltage
5
Step 5: If harness tests good, test neutral safety switch resistance across terminals in Park and Neutral positions per specifications
Estimated Repair Cost
$200 - $700
Parts + labor, varies by vehicle and location
The neutral safety switch circuit has a short to battery voltage, providing constant power when it should be a switched ground signal. This prevents the PCM from properly determining if the transmission is in Park or Neutral for starting safety interlock.
The most common cause of P1818 (Transmission Neutral Safety Switch Short Circuit To Battery) is: Damaged wiring harness with neutral safety switch wire shorted to power source
Typical repair costs for P1818 range from $200 to $700, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle may start in gear, creating serious injury risk. Vehicle may not start at all if PCM detects fault and disables starter circuit.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1818 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission Safety Interlock System
Difficulty
Type
Manufacturer
Recommended Tools
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