Chevrolet Citation U1859 Engine Trouble Code
What is Chevrolet Citation U1859?
When Chevrolet Citation 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 Chevrolet Citation
The Chevrolet Citation is particularly susceptible to U1859 faults when the engine management unit receives conflicting sensor data. Owners report that U1859 on Chevrolet Citation most commonly surfaces after 60,000 miles, especially when routine service intervals have been missed.
Code Information
| Code Type: | OBD-II Network (U) Trouble Code |
| System: | Network |
| Vehicle: | Chevrolet Citation |
| Brand: | Chevrolet |
| Model: | Citation |
| Code: | U1859 |
U1859 Chevrolet Citation Symptoms
Check Engine Light
Illuminated Chevrolet Citation dashboard warning
Engine Stalling
Engine stops unexpectedly or misfires
Performance Issues
Reduced power or acceleration on the Chevrolet Citation
Starting Problems
Difficulty starting the engine
Poor Fuel Economy
Increased fuel consumption on the Chevrolet Citation
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 Chevrolet Citation 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:
Most manufacturers number cylinders sequentially from front to back. Ford V-engines start with cylinder 1 at front left. In V-6 engines, cylinder 4 is front right; in V-8 engines, cylinder 5 occupies that position.
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.
Chevrolet Citation U1859 Repair Cost
On the Chevrolet Citation, secondary air injection pump replacement for a U1859 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.
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 Chevrolet Citation
A common error on the Chevrolet Citation is attributing U1859 to the crankshaft position sensor when the real fault is a damaged flywheel ring gear. The missing tooth pattern created by ring gear damage is intermittent and generates the same signal anomaly.
DIY Repair Guide: U1859 on Chevrolet Citation
When attempting DIY diagnosis of U1859 on your Chevrolet Citation, a smoke machine test is the gold standard for finding vacuum leaks. Rental tools are available from most auto parts stores for $0–$20/day, or you can fabricate a makeshift tester using a hand vacuum pump and soapy water spray.
Preventing U1859 on the Chevrolet Citation
For turbocharged Chevrolet Citation models, allowing the engine to idle for 60–90 seconds before shutdown after hard driving reduces turbocharger heat soak and prevents the coking of oil that blocks VVT galleries — a known secondary trigger of U1859.
Frequently Asked Questions — Chevrolet Citation U1859
A: Yes. Any stored fault code — including U1859 — will cause an automatic failure in most OBD-II based emissions tests. The code must be resolved and the vehicle must complete a full OBD drive cycle with no new codes before the test.