SPN 806 — ASR Valve, Differential 1
Drive with cautionEnough to reach the yard
Updated: 2026-11-14
J1939 code SPN 806. Below — how the fault is worded at the factory by Bendix ABS/ESP, Renault Trucks and WABCO ABS/ESC, and what the second half of the code (FMI) means in the standard.
How to check it yourself
The ASR (anti-slip regulation) valve of the driven axle: on command from the unit it engages the differential lock of the driven axle, so that one wheel does not spin.
What it should read
| ASR valve operation on command | yes, on switching — checked per diagnostics and on the bench |
| Valve inlet pressure | per the manufacturer's manual |
Check order
- FMI 3, 4, 5, 13 (short to supply or open circuit): unplug the valve with the ignition off and switch it on. If the code goes — the valve; if it stays — the wiring.
- Check the ASR valve pneumatically: supply present, but no pressure after the valve on command — the valve is not opening.
- Check the valve's joints for leaks with soapy water.
Common causes — from most to least frequent
- ASR valve with a sticking spool.
- Short to supply in the harness to the valve.
- Air leak at the valve joints.
- ABS modulator of the driven axle (per the Wabco factory line).
Bendix ABS/ESPRenault TrucksWABCO ABS/ESC
Bendix ABS/ESP
| FMI 3 | TCV DA Solenoid Shorted to Voltage |
| FMI 4 | TCV DA Solenoid Shorted to Ground |
| FMI 5 | TCV DA Solenoid Open Circuit |
| FMI 13 | TCV DA Configuration Error |
Renault Trucks
| FMI 2 | ASR valve, rear, does not meet requirements. Repair: Check that the ASR valve is the correct one. |
| FMI 3 | ASR valve supply, short circuit. Repair: Check the continuity of the ASR valve wiring (X4/4, X4/7). |
| FMI 4 | ASR valve supply, short circuit. Repair: Check the continuity of the ASR valve wiring (X4/4, X4/7). |
| FMI 5 | ASR valve supply, open circuit. Repair: Check the continuity of the ASR valve wiring (X4/4, X4/7). |
WABCO ABS/ESC
| FMI 3 | ABV Drive Axle. Shorted to UBATT |
| FMI 5 | ABV Drive Axle. Open Circuit |
| FMI 6 | ABV Drive Axle. Shorted to Ground |
What FMI means in J1939
Can I keep driving
Drive with caution. The ABS on this wheel or axle may be off, but the service brakes work. On a slippery road brake gently. Get it repaired soon.
What happens if you keep driving
The ABS on this wheel or axle may be out of action, while the service brakes still work. On a dry road you may notice no difference.
On a slippery road brake gently and keep a longer following distance. Do not put the repair off: if the red brake lamp comes on or the pedal feels soft, stop.
Nearby: other
- SPN 706Auxiliary Input/Output #06
- SPN 711Auxiliary Input/Output #11
- SPN 723Engine speed (auxiliary sensor)
- SPN 732Gas Metering Valve
- SPN 746Differential Lock Solenoid Valve #1
- SPN 920Audible Alarm
- SPN 925Auxiliary Output #2
- SPN 970Engine Auxiliary Shutdown Switch
- SPN 974Remote Accelerator Pedal Position
- SPN 979Remote PTO Preset Speed Control Switch
Related codes
- SPN 705Auxiliary Input/Output #05
- SPN 701Auxiliary Input/Output #01
- SPN 630Calibration Memory
- SPN 624Yellow Warning Lamp
- SPN 609Controller #2
- SPN 1041Start Signal Indicator
- SPN 1042Tractor/Trailer Electronic Interface
- SPN 1045Stop Lamp Switch #1
Makes with this code
What SPN 806 is
SPN 806 is the ASR valve, differential 1. ASR is the traction-control function of the brake electronics, and this is one of the solenoid valves it drives. In this database the number appears for Renault Trucks. The exact role of the valve depends on the brake system fitted, so use the make table above for its precise wording. The electronics check the valve coil and its wiring.
- SPN 806 FMI 5 - current below normal or open circuit: a broken wire, a corroded pin or a failed coil. This is the most common entry.
- FMI 6 - current above normal or shorted to ground: chafed wire or wet connector.
- FMI 3 and 4 - circuit voltage high or low.
- FMI 7 - the valve is not responding mechanically.
Checks
1. Read all brake codes. If supply or ground codes appear with it, fix those first.
2. Find the valve (the make manual shows where) and look at the connector for water and corrosion.
3. Measure the coil resistance (values are in the workshop manual; a few ohms to a few tens of ohms is typical for such solenoids). Infinite means open, near zero means shorted.
4. Wiggle the harness while watching the reading to find an intermittent break.
5. Replace the valve only when the coil and wiring are proven bad.
Can you keep driving?
Normal braking is not affected by this code alone. Traction control may be switched off, so starting on ice or wet ground is harder. Drive carefully and repair soon; the ABS function may also be limited on some systems.
Questions and answers
Why does a traction-control valve code turn on the ABS lamp?
On many systems ASR and ABS share the same electronic unit and valve block, so a fault in one lights the common lamp.
Is SPN 806 an engine fault?
No. It is a brake and traction system fault, although ASR does exchange torque requests with the engine.
Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.