Subaru H6 U1859 Engine Trouble Code
What is Subaru H6 U1859?
When Subaru H6 U1859 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.
U1859 on the Subaru H6
Service bulletins for the Subaru H6 specifically mention U1859 as a symptom of failed purge solenoid valves in the EVAP system. The solenoid body on this platform degrades in high-humidity environments and should be inspected whenever this code appears.
Code Information
| Code Type: | OBD-II Network (U) Trouble Code |
| System: | Network |
| Vehicle: | Subaru H6 |
| Brand: | Subaru |
| Model: | H6 |
| Code: | U1859 |
U1859 Subaru H6 Symptoms
Check Engine Light
Illuminated Subaru H6 dashboard warning
Engine Stalling
Engine stops unexpectedly or misfires
Performance Issues
Reduced power or acceleration on the Subaru H6
Starting Problems
Difficulty starting the engine
Poor Fuel Economy
Increased fuel consumption on the Subaru H6
Increased Emissions
Failed emissions test due to U1859
U1859 Code Structure
Understanding what each digit means in the U1859 network trouble code:
| U | 1 | 8 | 5 | 9 |
|---|---|---|---|---|
| Network Code | Fuel And Air Metering | Engine Oil Temperature Sensor Malfunction | Cylinder 1 Injector Circuit Low | Reverse Input Circuit |
How to Fix Subaru H6 U1859
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:
A/C pressure sensor monitors refrigerant pressure changes. DTC sets when pressure change falls outside calibration. Verify A/C system function, refrigerant charge, and electrical connections.
Technical Notes:
For U1859, verify VCT solenoid operation. Look for stuck or sticking valves caused by contamination. Consult vehicle-specific repair manual for proper component testing procedures.
Subaru H6 U1859 Repair Cost
Fuel injector cleaning service on the Subaru H6 costs $150–$300 for an ultrasonic bench-clean of all injectors with flow-test certification. On-car induction cleaning is a cheaper ($80–$120) first step but is less thorough for heavily fouled injectors.
U1859 Description
U1859 engine trouble code is related to Reverse Input Circuit.
Main Cause
The primary reason for U1859 OBD-II Engine Trouble Code is: Engine Oil Temperature Sensor Malfunction.
Common U1859 Misdiagnosis on the Subaru H6
Some Subaru H6 models have a known software bug where the PCM flags U1859 after battery disconnection and reconnect. Always perform an ECU adaptation reset and drive cycle before ordering any parts following battery work.
DIY Repair Guide: U1859 on Subaru H6
The Subaru H6 EVAP purge solenoid valve is accessible without lifting the vehicle — it is mounted on the intake manifold and secured by a single bolt and a vacuum hose clip. DIY replacement is rated 1/5 difficulty and takes approximately 20 minutes.
Preventing U1859 on the Subaru H6
The Subaru H6 coolant temperature sensor plays a role in fuel enrichment during warm-up. Replacing it as a precaution at 80,000 miles ($25–$40 DIY) prevents the faulty cold-start enrichment that can lead to U1859.
Frequently Asked Questions — Subaru H6 U1859
A: If your Subaru H6 is within the factory powertrain warranty period (typically 3–5 years or 60,000–100,000 miles depending on region and generation), U1859 repairs caused by component defects should be covered. Bring your service history to the dealer appointment.