SPN 3510 FMI 16: Meaning and Fix
SPN 3510 FMI 16 indicates the ECM detects Sensor Supply Voltage 2 above its normal operating range, typically exceeding 5.25V. This supply powers multiple 5V sensors. A common real-world scenario occurs after a jump-start with a 24V system on a 12V vehicle, instantly overstressing the internal regulator and logging this active fault.
Common Symptoms
- Erratic sensor data: Multiple sensors on supply 2 output implausible values, causing intermittent drivability issues.
- Illuminated MIL/CEL: Dashboard warning lamp activates immediately upon detecting the overvoltage condition.
- Torque derate active: ECM reduces engine power to protect components from potential overvoltage damage.
- Failed sensor cluster: All sensors sharing supply 2 (e.g., rail pressure, EGR position) may cease communication.
Probable Causes
- Shorted 5V reference: A sensor internal short pulls the 5V rail up to battery voltage through the ECM.
- Faulty ECM regulator: Internal voltage regulator failure allows unregulated voltage to the sensor supply circuit.
- Wiring harness damage: Chafed wires contacting 12V/24V power lines cause supply overvoltage.
- Aftermarket modifications: Improperly installed accessories backfeed voltage into the J1939 sensor supply network.
Advanced Technical Analysis
The ECM microcontroller continuously monitors the 5V supply rail via an internal analog-to-digital converter. When the sampled voltage exceeds 5.25V for more than 100 ms, the diagnostic debounce timer expires and FMI 16 is set. The threshold is calibrated per SAE J1939-71, with a hysteresis of 0.2V to prevent oscillation.
An overvoltage condition on Sensor Supply 2 typically originates from a short-to-battery in the harness. The ECM’s internal protection diode conducts, clamping the rail to roughly 5.8V before damage, but the diagnostic triggers before this. Real-world case: a crushed harness near the exhaust manifold on a Deutz TCD 2013 caused this fault.
Upon activation, the ECM invokes a torque derate strategy, reducing engine output by up to 40% to prevent sensor burnout. The derate is proportional to severity: at 5.5V, a 25% limit is applied; above 6.0V, the ECM may disable the fuel injection system entirely. This protects sensors like the Bosch RPS and MAF.
Long-term diagnosis requires isolating the supply circuit by disconnecting sensors one-by-one while monitoring voltage. In workshops, technicians often find a failed NOx sensor internal short. Prevention includes verifying all aftermarket devices are wired through relays, not directly to sensor power. Bosch manuals recommend a dedicated 5V supply check during annual PMs.
Step-by-Step Troubleshooting Guide
- Measure supply voltage: With ignition on, measure voltage at Sensor Supply 2 pin. Should be 4.9-5.1V.
- Disconnect sensors: Remove each sensor on supply 2 one at a time; if voltage normalizes, the last sensor is faulty.
- Inspect harness routing: Check for chafing near sharp edges or hot surfaces, especially near the engine block.
- Test ECM output: If all sensors disconnected still show >5.25V, replace the ECM due to internal regulator failure.