What Does P1278 Mean?
An open circuit has been detected between the high-side and low-side control circuits for cylinder #3's injector or coil system. This indicates a wiring or driver circuit problem.
Common Causes
35%
Open circuit in injector or ignition coil wiring for cylinder #3
30%
Faulty fuel injector or ignition coil
20%
ECM internal driver circuit failure
15%
Corroded or damaged connector terminals
Diagnostic Steps
1
Step 1: Inspect connectors for cylinder #3 injector and coil for damage or corrosion
2
Step 2: Test resistance of injector and ignition coil for cylinder #3
3
Step 3: Check continuity of wiring between ECM and cylinder #3 components
4
Step 4: Use oscilloscope to verify control signals from ECM
5
Step 5: Perform voltage drop test on ground circuits
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
An open circuit has been detected between the high-side and low-side control circuits for cylinder #3's injector or coil system. This indicates a wiring or driver circuit problem.
The most common cause of P1278 (Cylinder #3 High To Low Side Open) is: Open circuit in injector or ignition coil wiring for cylinder #3
Typical repair costs for P1278 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Engine will misfire on cylinder #3 causing rough running and power loss. Safe to drive short distances.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1278 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Fuel System / Ignition System
Difficulty
Type
Manufacturer
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
