2016 Dodge Challenger Check Engine Light? How to Diagnose and Fix

The Basics

The Check Engine Light (CEL) is a generic warning from your vehicle's onboard diagnostics (OBD-II) system that something is out of spec. It is not a diagnosis in itself, but a starting point for one. Based on an analysis of 99 owner discussions, the light is most commonly triggered by issues ranging from a loose gas cap to serious transmission or network communication faults. The two specific trouble codes mentioned in these reports are U0001 (High Speed CAN Communication Bus) and P0734 (Gear 4 Incorrect Ratio), which point to very different underlying problems.

What Drivers Experience

Owners report a wide spectrum of experiences when the CEL illuminates. The most common is simply seeing the steady yellow light on the dash with no noticeable change in vehicle performance. Others report the light flashing, which typically indicates a severe misfire requiring immediate attention. For those with specific codes, experiences vary:

• For P0734 (Transmission): Drivers often note harsh shifting, the vehicle seeming to "slip" out of gear, or a noticeable lack of power or acceleration, particularly in 4th gear.
• For U0001 (Network Communication): Symptoms can be intermittent and strange, including multiple warning lights, gauges dropping to zero or behaving erratically, and features like power seats or infotainment systems malfunctioning. One discussion specifically mentioned issues with a seat motor acting up in conjunction with network codes.

What Causes It

The causes are as varied as the codes themselves. Based on owner-reported fixes from the analyzed discussions:

1. Minor Issues (Most Common): A loose, damaged, or missing gas cap is a frequent culprit. Poor fuel quality or a simple misfire from old spark plugs also rank high.
2. Electrical & Sensor Failures: Faulty oxygen sensors, mass airflow sensors, or ignition coils are prevalent causes. For code U0001, the issue is often a faulty module on the Controller Area Network (CAN bus), damaged wiring, or a poor connection at a hub or gateway module.
3. Mechanical Problems: Code P0734 specifically points to a mechanical issue within the transmission. Common causes include low or degraded transmission fluid, a faulty solenoid, worn clutch packs, or internal valve body problems. In several discussions, using a specific Mopar diff slip additive was noted as a potential fix for certain transfer case or differential-related issues that could trigger drivetrain codes.
4. Simple Oversights: In multiple threads, the root cause was a simple error during DIY work, such as forgetting to reconnect a sensor after using a socket extension to reach a deep component.

Testing Procedures

Proper diagnosis is critical to avoid replacing good parts.

1. Scan for Codes: Use an OBD-II scanner to retrieve the specific trouble code(s). A generic P-code is just the start; note any pending codes as well.
2. Check the Obvious: Verify the gas cap is tight and the seal is intact. Perform a visual inspection for any disconnected wires or vacuum hoses, especially if recent work was done.
3. Live Data & Freeze Frame: Use a scanner that can view live data. For transmission code P0734, monitor gear command vs. actual gear ratio and transmission fluid temperature. For network code U0001, check for modules that are not responding.
4. Circuit Testing: For sensor-related codes, test the sensor's reference voltage, ground, and signal with a multimeter. For CAN bus issues, checking terminal tension at connector hubs and testing for short-to-power/ground on the CAN high and CAN low wires is essential.
5. Mechanical Inspection: For transmission issues, check the fluid level and condition. Burnt-smelling fluid indicates internal wear.

What Works

Solutions should be attempted in order of likelihood and cost, starting with the simplest.

1. Reset and Monitor (Low Cost): Tighten the gas cap, clear the code, and drive for a few days. If the light returns, the issue is persistent. This worked in numerous reports for intermittent lights.
2. Replace Common Wear Items (Medium Cost): Based on frequency in discussions, replacing fouled spark plugs, a faulty oxygen sensor, or a failing ignition coil resolves a significant percentage of CELs related to misfires and fuel trim.
3. Address Specific Faults (Variable Cost):
   • For P0734: Start with a transmission fluid and filter change. If the problem persists, solenoid replacement is the next logical step before considering internal transmission repairs.
   • For U0001: Systematically disconnect modules on the CAN bus to see if communication restores. Inspect and repair any corroded or damaged wiring, especially at junction points.
4. Professional Diagnostics (Higher Cost): For intermittent electrical faults or complex drivetrain issues, a shop with advanced scan tools and technical service bulletins (TSBs) for your specific model is often the most efficient path to a fix.

Budget Planning

Costs vary wildly based on the root cause.

• DIY (Minimal Parts): A new gas cap costs $15-$30. A basic OBD-II scanner is $30-$100. Common sensors (O2, MAF) range from $50-$250 for parts.
• DIY (Moderate Repairs): Transmission solenoid packs cost $150-$400. A set of ignition coils and plugs can be $200-$500. Transmission fluid service kits are $100-$200.
• Professional Repair: Shop labor runs $100-$150 per hour. A transmission solenoid replacement may cost $500-$900. Diagnosing and repairing a CAN bus fault (U0001) can take several hours, leading to bills of $300-$800+. Major internal transmission repair starts at $2,000 and can exceed $4,000.

Prevention Guide

Proactive maintenance is the best defense against a Check Engine Light.

1. Secure Fuel System: Always tighten the gas cap until it clicks three times.
2. Use Quality Fluids: Stick to recommended transmission fluid and consider periodic changes. Some owners in the data set preventatively used manufacturer-specific additives like Mopar diff slip additive where recommended.
3. Follow Service Intervals: Replace spark plugs, ignition coils, and air/fuel filters at the manufacturer's specified intervals.
4. Careful DIY Work: When working under the hood, be methodical. Keep track of all connectors and sensors, especially those removed using long socket extensions, and ensure they are firmly reconnected.
5. Address Minor Issues Promptly: A small vacuum leak or slightly rough idle can develop into a catalyst-damaging misfire. Don't ignore early warning signs.

Source Summary: This analysis is based on 99 owner discussions from Reddit and automotive forums.