Mitsubishi Sigma B1566 Engine Trouble Code
What is Mitsubishi Sigma B1566?
When Mitsubishi Sigma B1566 code appears, first check your gas cap. Pull over safely, ensure it is tight, and inspect for cracks. A loose or damaged gas cap affects fuel-system pressure and emissions. A replacement cap costs about $3–$10. This simple fix can resolve the code and improve fuel economy.
B1566 on the Mitsubishi Sigma
Independent workshop data shows that Mitsubishi Sigma vehicles with B1566 resolve approximately 40% of cases after a throttle body cleaning and idle relearn procedure. This is always the recommended first step before investing in new sensors.
Code Information
| Code Type: | OBD-II Body (B) Trouble Code |
| System: | Body |
| Vehicle: | Mitsubishi Sigma |
| Brand: | Mitsubishi |
| Model: | Sigma |
| Code: | B1566 |
B1566 Mitsubishi Sigma Symptoms
Check Engine Light
Illuminated Mitsubishi Sigma dashboard warning
Engine Stalling
Engine stops unexpectedly or misfires
Performance Issues
Reduced power or acceleration on the Mitsubishi Sigma
Starting Problems
Difficulty starting the engine
Poor Fuel Economy
Increased fuel consumption on the Mitsubishi Sigma
Increased Emissions
Failed emissions test due to B1566
B1566 Code Structure
Understanding what each digit means in the B1566 body trouble code:
| B | 1 | 5 | 6 | 6 |
|---|---|---|---|---|
| Body Code | Fuel And Air Metering | Fuel Composition Sensor Circuit Malfunction | Cylinder 4 Contribution/Balance Fault | Ignition Coil A Primary/Secondary Circuit Malfunction |
How to Fix Mitsubishi Sigma B1566
Diagnostic Steps:
Oxygen sensors measure exhaust gas oxygen content to optimise air-fuel ratio. This optimisation improves fuel economy and reduces emissions. Sensors degrade over time and require periodic replacement.
Repair Solution:
Power steering pressure switch monitors system operation. If pressure changes are not detected after calibrated speed transitions, this DTC sets. Verify PSP switch operation and check for circuit opens or shorts.
Technical Notes:
B1566 DTCs can be triggered by upstream issues. For example, a dirty MAF sensor may cause incorrect fuel-trim adjustments, leading oxygen sensors to report mixture problems. Address root causes first.
Mitsubishi Sigma B1566 Repair Cost
On the Mitsubishi Sigma, secondary air injection pump replacement for a B1566 code runs $350–$600. Because the pump is only active during cold starts, symptoms are easily missed. Requesting a cold-start emissions test at the workshop will confirm whether the pump is operating.
B1566 Description
B1566 engine trouble code is related to Ignition Coil A Primary/Secondary Circuit Malfunction.
Main Cause
The primary reason for B1566 OBD-II Engine Trouble Code is: Fuel Composition Sensor Circuit Malfunction.
Common B1566 Misdiagnosis on the Mitsubishi Sigma
When B1566 triggers on the Mitsubishi Sigma, a flashing check-engine light (as opposed to a steady one) indicates an active misfire. Misfire codes are commonly misdiagnosed as sensor faults; always rule out ignition and fuel delivery issues before testing sensors.
DIY Repair Guide: B1566 on Mitsubishi Sigma
Battery terminal cleaning on the Mitsubishi Sigma is a 5-minute job that resolves a surprising number of B1566 intermittents. Use a wire brush and a bicarbonate of soda solution to clean corrosion, then apply a thin coat of petroleum jelly to the terminals after refitting.
Preventing B1566 on the Mitsubishi Sigma
On the Mitsubishi Sigma, using a quality fuel system cleaner (added to the fuel tank every 10,000 miles) helps prevent injector deposit build-up that indirectly triggers B1566 through fuel-trim imbalances.
Frequently Asked Questions — Mitsubishi Sigma B1566
A: B1566 is a standardised OBD-II code that can appear on any make and model. However, the specific components and circuits that trigger this code, and the repair procedures involved, vary significantly between vehicles. The information on this page is focused on the Mitsubishi Sigma.