Subaru Forester 2 U1859 Engine Trouble Code
What is Subaru Forester 2 U1859?
The Subaru Forester 2 U1859 check-engine light can indicate issues ranging from minor (loose gas cap) to serious (catalytic converter failure). Professional diagnostic scanning at a dealer or shop will identify the exact cause and required repairs.
U1859 on the Subaru Forester 2
Owners who tow regularly with their Subaru Forester 2 should pay extra attention to U1859. The additional thermal load placed on the transmission fluid accelerates the degradation of the torque converter clutch solenoid, a frequent secondary cause of this code.
Code Information
| Code Type: | OBD-II Network (U) Trouble Code |
| System: | Network |
| Vehicle: | Subaru Forester 2 |
| Brand: | Subaru |
| Model: | Forester 2 |
| Code: | U1859 |
U1859 Subaru Forester 2 Symptoms
Check Engine Light
Illuminated Subaru Forester 2 dashboard warning
Engine Stalling
Engine stops unexpectedly or misfires
Performance Issues
Reduced power or acceleration on the Subaru Forester 2
Starting Problems
Difficulty starting the engine
Poor Fuel Economy
Increased fuel consumption on the Subaru Forester 2
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 Forester 2 U1859
Diagnostic Steps:
Check if fuel pump primes when key is turned to ON. Measure fuel pressure and verify bright white-blue spark at all plugs. Also verify mechanical timing alignment.
Repair Solution:
Excessive air inflow may result from vacuum leaks, dirty sensors, or EGR valves not closing properly. Insufficient fuel can stem from dirty injectors, clogged filters, weak fuel pump, or leaking pressure regulator.
Technical Notes:
U1859 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.
Subaru Forester 2 U1859 Repair Cost
Addressing U1859 on your Subaru Forester 2 typically involves: dealer diagnostic fee $95–$150, oxygen sensor replacement $180–$320 (parts + labour), or catalytic converter replacement $1,800–$2,400 if damage has progressed. Independent specialist garages often charge 20–30% less than franchised dealers for identical work.
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 Forester 2
When U1859 triggers on the Subaru Forester 2, 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: U1859 on Subaru Forester 2
The coolant temperature sensor on the Subaru Forester 2 is a straightforward DIY item (difficulty 2/5). Have a drain tray ready for the small amount of coolant that spills when the sensor is removed. Top up the cooling system afterwards and check for air pockets.
Preventing U1859 on the Subaru Forester 2
The Subaru Forester 2 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 Forester 2 U1859
A: Clearing the code without repair allows the fault condition to persist. Depending on the cause, this can lead to catalytic converter damage, increased fuel consumption, and secondary component failures that are significantly more expensive to address than the original fault.