What Does P1399 Mean?
The Engine Control Module detects that the engine RPM signal wire (typically from crankshaft or camshaft position sensor) is shorted to battery positive voltage. This prevents accurate engine speed monitoring and can cause multiple driveability issues.
Safety Warning
Vehicle may not start, stall without warning, or experience severe driveability issues. Do not drive until repaired as engine timing and fuel delivery are compromised.
Common Causes
45%
Damaged wiring harness causing short to power in crankshaft or camshaft sensor circuit
25%
Failed crankshaft position sensor with internal short
15%
Failed camshaft position sensor with internal short
10%
Connector pin corrosion or damage causing cross-circuit short
5%
Aftermarket accessory installation causing wiring damage
Diagnostic Steps
1
Step 1: Disconnect crankshaft and camshaft position sensors and check for voltage on signal wires (should be 0V with sensors disconnected)
2
Step 2: Inspect sensor wiring harness routing for damage, particularly near hot exhaust components or sharp edges
3
Step 3: Test sensor resistance and signal output voltage against manufacturer specifications
4
Step 4: Check for voltage backfeed at ECM connector terminals with sensors disconnected
5
Step 5: Perform wiggle test on harness while monitoring live data for signal dropouts
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
The Engine Control Module detects that the engine RPM signal wire (typically from crankshaft or camshaft position sensor) is shorted to battery positive voltage. This prevents accurate engine speed monitoring and can cause multiple driveability issues.
The most common cause of P1399 (Engine RPM signal, TD Short Circuit to B+) is: Damaged wiring harness causing short to power in crankshaft or camshaft sensor circuit
Typical repair costs for P1399 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle may not start, stall without warning, or experience severe driveability issues. Do not drive until repaired as engine timing and fuel delivery are compromised.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1399 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Management/Ignition System
Difficulty
Type
Manufacturer
Recommended Tools
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