SAGMOTO i9 Steering System Maintenance for the Electric Truck

The SAGMOTO i9 electric medium heavy truck delivers 245 to 410 kW peak from its permanent-magnet motors and carries a steering architecture that is fundamentally different from the hydraulic systems on diesel siblings, because the assist no longer draws from an engine-driven pump but from the 24V auxiliary bus and an electro-hydraulic unit.

Power steering architecture on the EV platform

The i9 routes steering assist through an electro-hydraulic pump that spins only when the steering wheel moves, so the parasitic loss that a diesel truck pays continuously at idle disappears and the battery range benefits on the Shenzhen distribution loop. The high-voltage traction pack is isolated from the steering circuit by design, and the assist motor draws from the 24V auxiliary battery that also feeds the air compressor and the body control module. Understanding this split matters because a steering complaint is often an auxiliary-battery complaint, and a technician who opens the high-voltage contactor looking for the fault wastes an hour. The rack itself is a recirculating-ball unit sized for the i9 gross combination weight up to 60 tonnes, and the valve spool is electronically damped to remove the kickback that an electric motor's instant torque would otherwise transmit through the column.

Electro-hydraulic steering unit checks

The electro-hydraulic unit on the i9 sits on the front frame rail beside the compressor, and its motor draws up to 40 A during a full-lock turn at the Port of Rotterdam terminal where the truck crab-steers between rows. Test the unit by turning the wheel lock to lock with the truck raised and the 24V bus healthy, and listen for a laboured whine that means low fluid rather than a failing pump because the reservoir shares the same mineral oil as the diesel rack. Bleed the loop through the bleed screw on top of the unit after any hose change, because an air pocket gives a soft centre and a groan on the first lock of the shift. Check the high-pressure hose for chafing where it runs past the HV conduit, because a rub-through sprays oil onto the traction harness and triggers an insulation fault that strands the truck.

Tie-rod end and drag-link inspection

The i9 front axle carries a drag link and a pair of tie-rod ends that wear the ball joints under the constant correction a driver makes in urban gridlock, because stop-start duty loads the joints in both directions every few seconds. Grease the joints every 20,000 km through the nipple and check for radial play with a pry bar, because a worn end lets the toe drift and scallops the inside edge of the front tyres within a month. The drag-link clamp bolts must be at the 110 Nm spec or the link rotates on the pitman arm and the steering wheel centre mark no longer matches the road, which the driver reads as the truck pulling. Replace ends in pairs so the geometry stays symmetric, and never re-torque a stretched clamp bolt because it will walk loose under the i9's regen braking loads that pulse the front axle harder than a coasting diesel.

Steering gearbox backlash adjustment

The recirculating-ball gearbox on the i9 has an adjustable worm preload that closes up as the balls wear, and too much backlash shows as a dead band at centre where the wheel turns five degrees before the road wheels answer. Adjust the preload screw on the top cover with the wheels straight and the front lifted, turning in until the wheel just binds, then backing off a quarter turn, because over-tightening the worm overheats the balls and seizes the box on a long motorway run. Measure the free play at the rim and keep it under 30 mm; beyond that the pitman arm slop lets the truck wander on the Nairobi expressway and the driver fights it all shift. Where the i9 shares a depot with the SAGMOTO i5 electric light truck the adjustment figures differ, so use the i9 manual and not the smaller truck's spec when setting preload.

Front-axle alignment and tyre wear

The i9 front axle is set to a slight toe-out that the regen torque biases toward toe-in as the load shifts forward under braking, and a tyre that wears the outside shoulder on both fronts points to a collapsed bush in the radius arm rather than a castor problem. Align the axle on a flat plate with the battery at half charge and the air suspension at ride height, because the i9's weight distribution changes with state of charge and a mis-set baseline gives a pull that varies through the day. The front tyres on urban i9 units scrub the edges at twice the rate of highway runners, so rotate the fronts to the rear tandem at 40,000 km and read the wear pattern as a steering-health report. Feathering across the tread blocks means the toe is cycling as the joints load, and that is a cue to re-check the tie-rod ends before the next alignment.

Low-voltage 24V supply impact on assist

Because the i9 steering assist depends on the 24V bus, a weak auxiliary battery on a cold morning in Harbin drops the assist motor voltage and the driver feels a heavy wheel that lightens once the DC-DC converter catches up. Watch the 24V gauge during a lock-to-lock sweep; a sag below 21V with the wheel held confirms the auxiliary battery or the DC-DC module rather than the rack. The high-voltage contactor closing also dips the 24V briefly, so a momentary heavy wheel at pull-away is normal, but a persistent one is not, and charging or replacing the auxiliary battery restores full assist.

Warning-code reading

The i9 logs steering faults under the chassis controller and raises a yellow steering icon when the assist motor current exceeds the limit or the angle sensor loses correlation with the road wheels. Read the codes with the SAGMOTO diagnostic tablet through the cab port and note that a stored over-current with no active fault usually means the driver held full lock against a kerb while parking, which is benign. A recurring angle-sensor mismatch after a wheel alignment means the zero point was not re-learned, and the re-calibration routine in the tablet resets the centre without parts. Clear only after confirming the 24V supply and the fluid level, because deleting a live over-temperature code hides a pump that is about to fail on the next long shift.

Urban duty and cold-climate steering feel

The i9 in city parcel duty steers hundreds of times per shift, and the electro-hydraulic unit's duty cycle is far higher than on a highway runner, so the fluid heats and the assist softens slightly by mid-shift, a feel the driver should expect rather than report. In cold climates the mineral oil thickens and the first lock of the morning is heavier until the unit warms, so spec the cold-grade fluid for fleets in the SAGMOTO new energy electric trucks range operating above the Arctic Circle. The instant torque of the electric driveline also means more kickback through the column on potholed city streets, and the electronic damping is tuned to absorb it, but a worn gearbox preload lets that kickback return, so keep the backlash in spec to preserve the calm urban feel.