Chevrolet Impala U1859 Engine Trouble Code
What is Chevrolet Impala U1859?
Chevrolet Impala U1859 indicates potential catalytic converter failure. If completely failed, your vehicle may not run properly and fuel economy will suffer significantly. Average replacement cost is $2,000–$2,140. This repair requires professional service and should not be delayed.
U1859 on the Chevrolet Impala
A known issue on the Chevrolet Impala is that aftermarket air filter upgrades can inadvertently trigger U1859. High-flow filters alter the intake resonance frequency, causing the MAP sensor to report pressure readings outside factory calibration.
Code Information
| Code Type: | OBD-II Network (U) Trouble Code |
| System: | Network |
| Vehicle: | Chevrolet Impala |
| Brand: | Chevrolet |
| Model: | Impala |
| Code: | U1859 |
U1859 Chevrolet Impala Symptoms
Check Engine Light
Illuminated Chevrolet Impala dashboard warning
Engine Stalling
Engine stops unexpectedly or misfires
Performance Issues
Reduced power or acceleration on the Chevrolet Impala
Starting Problems
Difficulty starting the engine
Poor Fuel Economy
Increased fuel consumption on the Chevrolet Impala
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 Impala U1859
Diagnostic Steps:
The catalytic converter has oxygen sensors before and after it. When warm and in closed-loop mode, the upstream O2 sensor reading should fluctuate, while downstream should remain steady.
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:
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.
Chevrolet Impala U1859 Repair Cost
VVT actuator replacement on the Chevrolet Impala for U1859 is a more significant investment: $400–$700 including the oil flush required before fitting the new actuator. Using the correct low-SAPS engine oil after the repair is critical to prevent premature re-failure.
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 Impala
A common error on the Chevrolet Impala 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 Impala
Replacing the oxygen sensor on the Chevrolet Impala requires an O2 sensor socket (22mm or 7/8") and penetrating oil applied 24 hours in advance. On vehicles over five years old, the sensor threads often corrode into the bung; heat from a propane torch (briefly applied) is usually sufficient to free them.
Preventing U1859 on the Chevrolet Impala
To keep the Chevrolet Impala free of recurring U1859 faults, change the engine oil every 5,000–7,500 miles using a grade specified by Chevrolet. Oil viscosity directly affects VVT actuator response, and using the wrong grade is one of the most avoidable causes of this code.
Frequently Asked Questions — Chevrolet Impala U1859
A: Almost certainly yes. Most faults that trigger U1859 cause the ECU to operate in open-loop mode or apply overly rich fuel trims, both of which increase fuel consumption by 5–15%. Resolving the fault promptly pays for itself in fuel savings over time.