P1278: Cylinder #8 Injector High-to-Low Side Open Circuit
The P1278 code indicates an open circuit between the high and low sides of the fuel injector for cylinder #8. This typically means the injector's internal coil is broken or there is a wiring issue between the injector and the engine control module (ECM). The ECM monitors the current flow through the injector circuit; when it detects an open, it sets this code. This can cause a misfire, rough idle, and reduced power.
01. Most Common Causes
- Faulty fuel injector on cylinder #8 (open internal coil)
- Open or shorted wiring in the injector harness
- Corroded or damaged connector at injector or ECM
- Failed ECM (rare)
02. Symptoms You Will Notice
- Misfire on cylinder #8
- Rough idle or engine shaking
- Check Engine Light illuminated
- Reduced fuel economy and power
03. Step-by-Step Diagnosis
Step 1: Scan for codes and confirm P1278. Check freeze frame data.
Step 2: Visually inspect injector #8 connector and wiring for damage or corrosion.
Step 3: Measure resistance across injector #8 terminals (should be 11-17 ohms). If open, replace injector.
Step 4: If injector resistance is good, check continuity from injector connector to ECM. Repair open circuit.
Step 5: Clear codes and test drive to verify repair.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with a misfire can damage the catalytic converter and cause poor performance.
How much does it cost to fix?▼
Replacing a fuel injector typically costs $150-$400 including parts and labor. Wiring repairs may be less.