2017 Dodge Ram Check Engine Light? Diagnose Radio Hub Issues

The Basics

A Check Engine Light (CEL) is a generic warning from your vehicle's onboard diagnostics system (OBD-II) that it has detected a fault. It is not a diagnosis in itself, but a prompt to investigate. The light can indicate issues ranging from a loose gas cap to serious engine or transmission problems. Based on owner reports, the two most common diagnostic trouble codes (DTCs) associated with this general alert in the analyzed data are U0402 (Invalid Data Received from Transmission Control Module) and P0733 (Gear 3 Incorrect Ratio).

What Drivers Experience

Owners reporting a CEL describe a wide range of accompanying symptoms, which are crucial for diagnosis. Many report the light coming on solid, not flashing, with no immediate change in drivability. Others experience more direct problems: erratic or inaccurate readings from gauges like the speedometer or tachometer, transmission issues such as harsh shifting or being stuck in a single gear (often linked to code P0733), and intermittent electrical gremlins. Several discussions mentioned issues starting the vehicle or with the ignition key cycle not engaging systems properly. Notably, some owners mistakenly associated unrelated modifications like rollbars or a front passenger tire issue with triggering the light, highlighting how the CEL can cause concern over any recent change to the vehicle.

What Causes It

Based on the cross-analysis of 83 owner discussions and the specific codes mentioned, causes fall into clear categories:

1. Transmission/TCU Communication Faults (Code U0402): This is often a wiring or module communication issue. Faults can stem from damaged wiring harnesses, poor connections at the Transmission Control Module (TCM), or a failing TCM itself. It indicates the engine computer isn't getting valid data from the transmission computer.
2. Mechanical Transmission Problems (Code P0733): This code points to a physical issue within the transmission. Common culprits include faulty shift solenoids, worn clutch packs or bands, low or degraded transmission fluid, or a defective valve body.
3. Electrical & Ground Issues: A significant number of resolved cases pointed to bad grounds or corroded battery terminals. These can cause voltage spikes or drops that confuse multiple control modules, leading to various codes and gauge malfunctions.
4. Faulty Sensors & Components: While less frequent in this dataset, common CEL triggers include failed oxygen sensors, mass airflow sensors, ignition coils, and a loose or faulty fuel cap.
5. Aftermarket Part Interference: Specific mentions of Pollak brand connectors and other aftermarket electrical parts suggest compatibility or installation issues can sometimes induce communication errors between modules.

Testing Procedures

Proper diagnosis is essential to avoid replacing good parts. Follow this sequence:

1. Scan for Codes: Use an OBD-II scanner to retrieve all stored codes. Don't just note the first one. Codes U0402 and P0733 provide a direct starting point. Also check for pending codes.
2. Check the Simple Things First: Verify the gas cap is tight. Inspect the battery terminals and major engine ground straps for corrosion or looseness. Clean and tighten as necessary.
3. Live Data & Freeze Frame: Use your scanner to view live data. For P0733, monitor vehicle speed, engine RPM, and commanded gear to see the discrepancy. For U0402, check communication status with the TCM.
4. Visual Inspection: Trace the wiring harness from the TCM and Engine Control Module (ECM) for any chafing, cuts, or rodent damage. Check connectors for pushed-out pins, corrosion, or moisture.
5. Component Testing: For transmission solenoids (suspected with P0733), resistance can be checked with a multimeter per the vehicle's service manual. Transmission fluid level and condition should be checked (color, smell).
6. Voltage & Communication Check: For communication codes like U0402, a professional scan tool or oscilloscope may be needed to check the network voltage on the CAN bus lines.

What Works

Solutions are ranked by the frequency of success reported in discussions, starting with the most common and cost-effective.

1. Address Electrical Foundations (High Success Rate): In numerous cases, simply cleaning and securing battery terminals and engine grounds resolved intermittent CELs and gauge issues. This is always the recommended first step.
2. Diagnose & Repair Wiring/Connectors: For communication code U0402, repairing damaged wires, cleaning connector contacts, or replacing a faulty Pollak or other aftermarket connector often fixed the problem.
3. Transmission-Specific Repairs (for P0733):
   • Fluid Service: A drain-and-fill with the correct fluid resolved some early-stage P0733 codes caused by dirty fluid.
   • Solenoid Replacement: The most common mechanical fix for P0733 was replacing the shift solenoid pack, often a DIY-able job with pan removal.
   • Valve Body Repair/Replacement: Required for more persistent shifting issues.
   • Transmission Overhaul/Rebuild: The last-resort solution for major internal mechanical failure.
4. Module Replacement: In a minority of cases for U0402, replacing the TCM or, rarely, the ECM was necessary after all wiring was confirmed good.
5. Ignition Cycle Reset: Some owners reported the light turning off after a specific key-cycle procedure (e.g., key to ON for 30 seconds, off, then start), which can reset modules after an electrical glitch is fixed.

Budget Planning

Costs vary dramatically based on the root cause and who does the work.

• DIY Electrical Fix (Grounds/Battery): $0 - $20 for cleaning supplies or a new terminal.
• DIY Wiring Repair: $20 - $100 for a wiring repair kit, solder, and heat shrink.
• DIY Transmission Solenoid Pack: $150 - $400 for parts (fluid and gasket included). Requires mechanical confidence.
• Professional Diagnosis: $100 - $200 for shop time to pull codes and pinpoint the issue.
• Professional Transmission Solenoid Service: $400 - $800 (parts and labor).
• Professional Valve Body Service: $800 - $1,500.
• TCM/ECM Replacement & Programming: $500 - $1,200+ at a shop, including part and programming.
• Transmission Rebuild: $2,500 - $4,500+.

Recommendation: Invest in a basic OBD-II scanner ($30-$100). Start with the free/cheap electrical checks. If the code points to a transmission solenoid, a DIY repair can save substantial money if you're equipped. For complex diagnosis (U0402) or internal transmission work, professional help is advised.

Prevention Guide

Preventing a CEL is about maintaining electrical and mechanical integrity.

1. Maintain Electrical Health: Periodically clean battery terminals and check that engine ground straps are tight and free of corrosion.
2. Use Caution with Aftermarket Parts: When installing electrical accessories, ensure they are high-quality and properly installed. Solder and heat-shrink wiring connections instead of using crimp caps.
3. Follow Service Intervals: Adhere to the manufacturer's schedule for transmission fluid service. This is critical for preventing solenoid and clutch wear that leads to codes like P0733.
4. Address Issues Promptly: A solid CEL should be investigated within a few days. A flashing CEL indicates a severe misfire and requires immediate attention to prevent catalytic converter damage.
5. Secure Wiring: After any under-hood work, ensure wiring harnesses are properly clipped and routed away from hot or moving parts.

Source Summary: This analysis is based on 83 owner discussions from Reddit and automotive forums.