What are the most likely causes of SPN 84?

Wheel speed sensor; Sensor wiring/connector

How do you diagnose code SPN 84?

1) Compare wheel speed signals at road speed

What part is usually replaced for SPN 84 and how much does it cost?

Wheel speed sensor: $40–$180 USD (aftermarket to dealer), plus 0.5–1.5 h of labor.

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SPN 84

CAUTION

Wheel-based vehicle speed

The truck's control module (ECU) reports a fault on: Wheel-based vehicle speed.

SPN 84 means a truck control module (ECU) flagged a fault on wheel-based vehicle speed, part of the Chassis system on heavy-duty diesel trucks. DERATE rates it CAUTION: you can keep driving carefully, but get it checked soon. Part usually replaced: Wheel speed sensor, $40–$180 (aftermarket to dealer) plus 0.5–1.5 h labor.

Chassis

Can I keep driving?

Yes, carefully. It does not usually cut power, but get it checked soon.

Most likely causes

Wheel speed sensor
Sensor wiring/connector

Recommended tests

1. Compare wheel speed signals at road speed

Part usually replaced

Wheel speed sensor

$40–$180 (aftermarket to dealer)

Labor: 0.5–1.5 h

USD, part only. Labor is billed at the shop's hourly rate.

Data: DERATE verified base, updated October 2026

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