What is Hyundai R455LC-7 Fault Code P191-16?

Fault Code P191-16 indicates a CAN communication error between the Engine Control Module (ECM) and the Machine Control Unit (MCU) on the Hyundai R455LC-7 excavator. This diagnostic trouble code specifically signals that the Controller Area Network (CAN) datalink has experienced a moderate-level failure condition, with the "-16" suffix denoting a voltage issue or intermittent communication loss on the CAN high or low circuit.

This code is critical for the R455LC-7's operation because the CAN bus serves as the central nervous system connecting all electronic control modules. When communication breaks down between the ECM and MCU, the excavator cannot properly coordinate engine performance with hydraulic demands, potentially triggering derate modes or complete shutdown to prevent machine damage. On used excavators, this fault often stems from aging wiring harnesses, corroded connectors, or ECU pin corrosion rather than catastrophic component failure.

Common Symptoms

• Yellow or red warning lights illuminated on the instrument cluster, often accompanied by a "Check Engine" or communication error message on the monitor panel
• Engine derating or power reduction mode activated, limiting RPM to 1,200-1,500 range regardless of throttle input
• Intermittent loss of instrument panel data, such as engine temperature, fuel level, or hydraulic pressure readings flickering or disappearing
• Erratic hydraulic system behavior, including inconsistent swing speed or boom response due to disrupted load-sensing communication
• Multiple secondary fault codes appearing simultaneously as other modules lose ECM communication

Potential Causes

The most common technical causes for P191-16 on used R455LC-7 excavators include:

• CAN bus wiring harness damage at known rub points near the turntable area where the main harness passes through the center joint, particularly common after 5,000+ operating hours
• Corroded or moisture-contaminated connector pins on the 38-pin ECM connector (located on engine right side) or the MCU connector behind the operator's seat
• Failed termination resistor (120-ohm) in the CAN network, typically located at either the ECM or display panel
• Voltage supply issues to either control module, often caused by failing alternator output or poor battery ground connections on aging machines
• ECM or MCU internal failure, though less common; more frequent on machines exposed to extreme temperature cycling or water intrusion events

How to Troubleshoot and Fix Code P191-16

Step 1: Verify Power Supply and Grounds Using a digital multimeter, check battery voltage at both the ECM (should read 24V ±2V with key on) and MCU. Inspect all ground connection points, particularly the engine block ground strap and chassis grounds near the battery box. On used excavators, corrosion at ground terminals is frequently overlooked but causes 30% of communication faults.

Step 2: Inspect CAN Bus Wiring and Connectors Physically trace the CAN high (typically yellow) and CAN low (typically green) wires from the ECM through the turret area to the MCU. Check for harness wear at the swing bearing pass-through—a notorious failure point on the R455LC-7. Disconnect connectors and inspect pins for green corrosion, bent terminals, or moisture. Clean with electrical contact cleaner and apply dielectric grease before reconnection.

Step 3: Test CAN Bus Resistance With key off and both ECM and MCU connectors disconnected, measure resistance between CAN high and CAN low terminals. You should read approximately 60 ohms (two 120-ohm termination resistors in parallel). A reading of 120 ohms indicates one termination resistor has failed; infinite resistance suggests an open circuit in the wiring.

Step 4: Use Diagnostic Software Connect Hyundai Hi-Mate or compatible diagnostic software to the service port. Monitor live CAN bus voltage (should fluctuate between 2.5-3.5V) and check for communication packet errors. This identifies whether one module is failing to respond or if wiring is causing signal degradation.

Step 5: Check for Previous Repairs On used machines, inspect for aftermarket splices, electrical tape repairs, or non-OEM connectors—common shortcuts during previous ownership that cause intermittent faults. Replace any compromised harness sections with OEM parts to ensure proper shielding and wire gauge.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Hyundai service manual and consider professional diagnostic assistance for complex electrical issues, especially when working with high-value used equipment.