What Does P0418 Mean?
The PCM has detected a short circuit condition in the secondary air injection switching valve B circuit. This code specifically indicates the signal voltage is being pulled low or the circuit current is excessive, pointing to a short to ground or an internally shorted component. The AIR system cannot properly direct air into the bank 2 exhaust manifold during cold starts. The driver will see the MIL but experience no performance changes.
Common Causes
35%
Chafed or melted wiring shorted to chassis ground near exhaust components
30%
AIR switching valve B solenoid with shorted windings
20%
Connector pin-to-pin short from contamination or bent terminals
15%
PCM output driver transistor failure
Diagnostic Steps
1
Disconnect valve B and measure solenoid coil resistance. Values well below the 20-40 ohm specification confirm shorted windings. Replace the valve assembly.
2
With the valve disconnected, check each wire at the harness connector for resistance to ground. Both should read OL (open line). Low readings pinpoint a harness short.
3
Visually trace the wiring harness from valve B to the PCM connector. Focus on areas near exhaust components, sharp metal edges, and harness pass-throughs where insulation can wear.
4
If the harness is clear, reconnect and command the AIR system on. Monitor current draw with an inductive current clamp — normal is 0.5-1.0A. Draws above 2A confirm a short-circuit condition.
5
Check if the fault only occurs when the engine is hot by monitoring PID data for the AIR system status during cold-start sequences on consecutive drive cycles.
Estimated Repair Cost
$120 - $450
Parts + labor, varies by vehicle and location
The PCM has detected a short circuit condition in the secondary air injection switching valve B circuit. This code specifically indicates the signal voltage is being pulled low or the circuit current is excessive, pointing to a short to ground or an internally shorted component. The AIR system canno...
The most common cause of P0418 (Secondary Air Injection System Switching Valve B Circuit Shorted) is: Chafed or melted wiring shorted to chassis ground near exhaust components
Typical repair costs for P0418 range from $120 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving. The short may blow the fuse protecting this circuit, but there is no risk to vehicle safety or driveability. Emissions testing will fail with this code present.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0418 to identify the root cause.
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Quick Info
Category
Powertrain
System
Emission Control System
Difficulty
Type
Generic (SAE)
Recommended Tools
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