Marathon Corsaire U1859 Engine Trouble Code
What is Marathon Corsaire U1859?
Marathon Corsaire U1859 code can indicate a faulty oxygen sensor, which may eventually damage the catalytic converter (repair cost: $2,000–$2,200). Professional diagnosis costs around $200–$210. Oxygen sensors are often straightforward to replace — check your owner's manual for location and instructions. This issue should be addressed promptly to prevent further damage.
U1859 on the Marathon Corsaire
The Marathon Corsaire ECU flash version prior to the 2.4.1 update has a known calibration bug that can generate spurious U1859 codes under hard deceleration. Verifying the ECU software version is always the first step before any mechanical diagnosis on this model.
Code Information
| Code Type: | OBD-II Network (U) Trouble Code |
| System: | Network |
| Vehicle: | Marathon Corsaire |
| Brand: | Marathon |
| Model: | Corsaire |
| Code: | U1859 |
U1859 Marathon Corsaire Symptoms
Check Engine Light
Illuminated Marathon Corsaire dashboard warning
Engine Stalling
Engine stops unexpectedly or misfires
Performance Issues
Reduced power or acceleration on the Marathon Corsaire
Starting Problems
Difficulty starting the engine
Poor Fuel Economy
Increased fuel consumption on the Marathon Corsaire
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 Marathon Corsaire U1859
Diagnostic Steps:
Regarding U1859, carefully inspect the wire harness near the intake manifold bracket, best accessed from below near the oil filter. Look for chafing, pinching, or damaged insulation.
Repair Solution:
Disconnected, dirty, or fouled spark plugs commonly prevent proper engine operation. Replace spark plugs every season or 25 hours. Verify proper spark plug gap. If plugs are good, check ignition components: spark plug wires, coils, and ignition module.
Technical Notes:
Parts or components should not be replaced based solely on U1859 DTC. Consult your vehicle service manual for proper diagnostic procedures, possible causes, and required testing before replacement.
Marathon Corsaire U1859 Repair Cost
A Marathon Corsaire U1859 fault caused by ignition coil failure costs roughly $90–$160 per coil including labour. Replacing all coils simultaneously — rather than one at a time — is recommended because coils typically age at similar rates. This preventive approach keeps total cost below $500.
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 Marathon Corsaire
Workshop technicians sometimes replace the entire ignition coil assembly on the Marathon Corsaire when U1859 accompanies a cylinder-specific misfire. In many cases, only the spark plug in the misfiring cylinder has fouled; a $8 plug replaces a $140 coil pack.
DIY Repair Guide: U1859 on Marathon Corsaire
The coolant temperature sensor on the Marathon Corsaire 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 Marathon Corsaire
After any fuel system repair on the Marathon Corsaire, always perform a fuel-trim reset and adaptation drive. Skipping this step leaves the ECU operating on pre-repair learned values, which can generate false U1859 alerts for weeks after the fix.
Frequently Asked Questions — Marathon Corsaire U1859
A: Contaminated or low-octane fuel can temporarily trigger U1859 through knock retard and lean/rich excursion events. If the code appeared shortly after a fill-up at an unfamiliar station, running the tank close to empty and refuelling with premium is a sensible first step.