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What the 37700-HN5-M51 Speed Sensor Does

The 37700-HN5-M51 Speed Sensor is the vehicle speed sensor (VSS) for the Honda Rancher 350 TRX350, model years 2000-2006. Honda lists 37700-HN5-M51 as an active part with no supersession, so ordering by this OEM number gets you the current revision.

Inside is a latching Hall-effect IC with a neodymium magnet (NdFeB, grade N42SH). The output is a 0-5V square wave at 4 pulses per wheel revolution, roughly 53.3 Hz at 20 mph on the stock 25-inch tires. The Honda PGM-FI/PGM-IG ECU reads that signal for speedometer drive and circuit monitoring.

Quick facts

• Fits TRX350TE, TRX350TM, TRX350FE, and TRX350FM (2000-2006).
• Plug-and-play: the air gap of 0.5 to 1.5 mm is fixed by the OEM mounting boss, so no calibration is needed.
• Readable by 2026 CAN-bus 3.0 hybrid scan tools through legacy VSS PID $0D mapping.
• IP68 sealed: 1-meter submersion for 30 minutes per ISO 20653:2023.

Want a second source before you buy? Koeep also lists this part as Speed Sensor for Honda Rancher 350 TRX350 2000-2006 ATV Models, with the same 2000-2006 fitment range.

37700-HN5-M51 Specifications

These values describe the 2026 production revision, cross-referenced against OEM engineering databases and ISO/SAE standards.

Build: Housing, Sealing, and Electrical Protection

The 2026 protocol aligns with ISO 20653:2023 ingress protection (IP67 minimum) and SAE J1455 environmental testing for off-highway use, with continuous operation rated from -40°C to +150°C under SAE J1211 thermal cycling.

Housing and connector

The housing is injection-molded PPS-GF40, a 40% glass-fiber-reinforced polyphenylene sulfide. It replaces earlier PA66 nylon that suffered hydrolytic degradation in humid conditions. The connector body is an ASA+PC alloy rated UL 94 V-0.

The 3-pin Sumitomo HM-series sealed connector uses gold-plated phosphor-bronze terminals and dual silicone wire seals. Contact resistance stays below 0.5 mΩ after 100 mate/demate cycles per USCAR-2 Revision 7.

Sensor element and safeguards

The Hall IC follows the Allegro A1210-series architecture, with reverse-battery protection to -24V DC, an overvoltage clamp at 28V DC, and short-circuit protection on the signal line. That matters when a powered scan tool back-probes the circuit.

Output impedance is 1.2 kΩ ±10%. For voltage-drop testing, use a DMM with more than 10 MΩ input impedance so the meter does not load the signal line and skew the reading.

DTC Mapping for the TRX350 Sensor Circuit

The TRX350 does not natively broadcast SAE J1979 OBD-II. Bridge modules such as the Honda MCS-01 interface translate the ECU's fault registers into standardized codes. Four DTCs in the P0500-P0503 range (SAE J2012) map to this circuit:

• P0500: VSS "A" circuit malfunction. Open circuit, short to ground, or short to V-Batt on the signal wire (blue/white on the TRX350 wiring).
• P0501: VSS range/performance. Implausible signal, such as 0 mph at over 3,500 RPM in gear. Often an air gap beyond 2.0 mm.
• P0502: VSS circuit low input. Signal voltage below 0.8V. Check for chafed wiring on the frame rail near the steering stem.
• P0503: VSS intermittent/erratic/high. Spikes or dropouts over 500 ms. Usually corroded HM terminals or a cracked pole piece.
• Honda Blink Code 11: speed sensor no-signal on pre-2004 models. The needle sits at zero and the odometer freezes.

Cross-platform diagnostics: the sensor maps to Mode $01 PID $0D (vehicle speed) and Mode $06 TID $41 (VSS circuit monitor), which Ford IDS, GM GDS2, and Toyota Techstream adapters read in 2026 workflows.

Scan Tool Compatibility

The analog Hall pulse train works with 2026 OBD-II/CAN hybrid scan tools through waveform analysis and legacy VSS PID mapping on the ISO 11898-1:2024 physical layer. Verified pairings:

• Autel MaxiSYS MS919 (waveform library v4.2 or newer)
• Snap-on ZEUS+ (guided component test for Honda VSS)
• Bosch ADS 625X (VSS signal simulation mode)
• PicoScope 7 Automotive (preloaded 37700-HN5-M51 waveform reference)

All four identify the 4 PPR signature at known wheel speeds once you select the Honda TRX350 vehicle profile.

OEM Cross-Reference

The 37700-HN5-M51 is Honda-specific, but its latching Hall IC with 0-5V open-collector output shares a core design with the Ford F-series VSS (F85Z-9E731-AA), the GM/ACDelco 213-4709 speed sensor, and the Toyota 83181-12040 magnetic pickup. That topology remains the dominant speed-sensing design across Polaris, Can-Am (BRP), and Yamaha.

The 4 PPR / 50% duty cycle output is the de facto standard for off-highway speedometer drive. It pairs with 2026 digital dashboards from Trail Tech, Koso, and AIM Sports, and with aftermarket ECUs from Haltech, MoTeC, and MaxxECU through their digital frequency inputs.

Why generic sensors fail here

Two-wire VR (variable reluctance) sensors are not electrically compatible with the TRX350 ECU, which expects a powered three-wire Hall signal. Off-brand units often output 2 or 8 PPR instead of 4, so the speedometer reads exactly 50% or 200% of true speed. That error silently skews odometer-based service intervals.

This replacement matches the OEM magnetic flux density (45-55 mT at a 1.0 mm air gap), the slew rate (rise and fall in 10 μs or less), and the Sumitomo pinout. Materials meet RoHS 3 (EU 2025/863) and REACH SVHC rules: lead-free solder, cadmium-free plating, and no DEHP, DBP, BBP, or DIBP phthalates.

Power Supply and LiFePO4 Notes

The 4.5V to 16V supply range covers the 13.2V to 14.6V nominal output of LiFePO4 ATV batteries. Measure the battery's BMS output for ripple above 50 mV peak-to-peak on the 12V rail.

If you find ripple, fit a 2,200 μF / 25V electrolytic capacitor across the sensor supply pins or use an isolated DC-DC regulator. LED lighting and USB charging circuits on restored machines add noise, so the check is worth five minutes.

Related Parts and Ordering Help

Refreshing more than one sensor? Koeep also carries the Oil Temperature Sensor for Honda 350 Rancher 400 450 Foreman TRX500 (37750-HC4-751), so you can bundle the wear items for the same Honda utility platform.

Electrical parts catalog

Connector repairs, ECU swaps, and wiring work around this install belong in the Starters, Alternators & ECUs collection, Koeep's full electrical catalog.

Talk to a person

Shop and fleet orders go through the request-for-quote page. For a quick fitment check, message support on WhatsApp or write to support@koeep.com.

More on the blog

Working on trucks too? The koeep blog covers the front ball joint, pitman and idler arm kit for Chevy & GMC C2500/C3500, a steering wear fix for those platforms.

Frequently Asked Questions