2002-2006 Infiniti Q45 ABS Light On: Common Causes and Fixes

By Core Brake Parts Tech Team — Circleville, OH warehouse

When the ABS light stays on in a 2002-2006 Infiniti Q45, the anti-lock function has shut itself off and the car is braking on its base hydraulics alone. On this car the usual culprits are a wheel speed sensor or its wiring, a damaged sensor ring or worn hub, low brake fluid, or a fault inside the ABS/VDC actuator. Because the Q45's stability control shares that hardware, the ABS light usually arrives with the VDC and SLIP lights too.

How the ABS and VDC System Works on the Q45

Infiniti's press material for the 2003 Q45 lists 4-wheel vented disc brakes with 4-wheel ABS, Electronic Brake force Distribution (EBD) and Brake Assist, plus Vehicle Dynamic Control (VDC) as standard on every Q45. VDC controls brake pressure and engine torque on its own when the car understeers, oversteers or hits a slippery surface. All of these features depend on the same inputs: a speed signal from each of the four wheels, a healthy hydraulic actuator, and enough fluid in the master cylinder reservoir.

That shared design is why one bad input can light several lamps at once. If the control unit loses a wheel speed signal it cannot tell whether that wheel is locking or spinning, so it disables ABS, and usually VDC and traction control with it, and turns on the warning lights. Normal braking still works, but you lose anti-lock control in a panic stop or on a slick road, and on this rear-drive V8 sedan you also lose the stability system.

Common Causes of an ABS Light on a 2002-2006 Q45

Wheel speed sensors and tone rings

Speed sensors sit right next to the brakes and hub, so they live in brake dust, water and road debris. Brake and Front End magazine notes that metallic debris sticking to the sensor tip, a damaged tone ring, or too wide an air gap between sensor and ring can all weaken the signal, and even a small nick in the ring can disrupt it. A pinched or chafed wire near the knuckle or rear subframe does the same thing, and that often shows up right after someone has done brake, suspension or hub work.

Hubs and bearings

The sensor reads a toothed ring or encoder that turns with the hub. If the bearing develops play, the gap between the ring and sensor changes as the wheel turns and the signal becomes uneven. A Q45 with a humming wheel bearing and an ABS light should have the bearing checked before anyone buys a sensor.

Brake fluid level

Fluid drops as the pads wear, because the caliper pistons move out and hold more fluid. A low reservoir is often a sign of worn pads rather than a leak, but either way the low level can trigger warnings. Top up only with the brake fluid type printed on the reservoir cap or in the owner's manual, and do not overfill a system that still has worn pads in it, because the level will rise when new pads push the pistons back.

How to Diagnose It

1. Check the fluid level and the red brake light. If the red BRAKE lamp is also on and fluid is low, stop there and find out why before driving far. Inspect pad thickness and look for wet spots at each wheel and at the master cylinder.
2. Scan for codes with a tool that reads ABS. A basic engine-code reader will not see the ABS/VDC module. The code will point to a specific wheel sensor, the pump motor, a solenoid, or supply voltage.
3. Confirm the code before buying parts. Brake and Front End warns that pulling a sensor code does not mean you should immediately replace the sensor. Look at live wheel speed data while driving slowly: one wheel reading zero or dropping out points to that corner.
4. Inspect the corner. Pull the sensor, clean the tip, check the wire along its full run, and look at the tone ring for cracks, rust scale or missing teeth. AA1Car describes testing passive sensors by AC voltage output while spinning the wheel, or with an oscilloscope, which shows dropouts a meter can miss.
5. Check the hub. Rock the wheel at 12 and 6 o'clock with the car safely on stands. Any play or roughness means the bearing may be the real problem.
6. Clear codes and road test. Many sensor faults only reset after the car sees wheel speed again, so the light may stay on until you drive a short distance.

Recalls: What Applies to the Q45 and What Does Not

NHTSA's recall records for the 2002 through 2006 Q45 show no recall for the ABS unit itself. The 2004 Q45 does carry recall 04V497000 for a brake lamp switch that may malfunction so the brake lights do not come on when you brake, and the 2003-2005 cars carry 12V079000 for a side air bag connector. If you own a 2004, run the VIN through Infiniti or NHTSA to confirm the switch was replaced. A working brake switch matters for the brake lights regardless of any ABS symptom.

You may also see an Infiniti notice telling owners not to drive with the ABS light on because the actuator can leak. That recall covers certain 2017 QX60 vehicles, not the Q45, so it does not explain an ABS light on a 2002-2006 Q45.

What to Replace at the Same Time

ABS lights often show up around brake jobs, so it is smart to fix both sides of the problem at once:

• Pads and rotors: if the fluid was low because the pads are worn, replace the pads and inspect the rotors. For the front axle we carry drilled and slotted front rotors for the 2002-2006 Q45, and you can pair them with ceramic brake pads.
• Hardware: new clips and slide pin boots from our brake hardware kits keep the pads from dragging, which also reduces brake dust building up on the sensors.
• Flexible hoses: on a car this age, the rubber hoses at each corner are worth inspecting while the wheels are off. See brake hoses.
• Fluid: brake fluid absorbs moisture over time. If it is dark, a flush with the correct fluid is cheap insurance for the ABS actuator's internal valves.

Be careful when removing the rotors and calipers: route the sensor wire out of the way and do not let the caliper hang on the hose or pull on the sensor harness.

How Hard Is the Job?

Checking fluid and reading codes is easy for any owner with an ABS-capable scan tool. Replacing a wheel speed sensor is a moderate driveway job if the old one comes out cleanly, but on older cars sensors often seize in the knuckle and need patience and penetrating oil. A hub or bearing replacement is a bigger job. Actuator faults, and any job that opens the ABS hydraulic circuit, usually need a scan tool that can run the pump and bleed routine, so most owners leave those to a shop. Torque every fastener to the values in the factory service manual.

Frequently Asked Questions

Is it safe to drive a Q45 with the ABS light on?

The base brakes still work, but anti-lock control and usually VDC are off, so stops on wet or icy roads are less controlled. If the red BRAKE light is also on or the pedal feels different, have it checked before driving.

Why do the ABS, SLIP and VDC lights all come on together?

The Q45's ABS, traction control and VDC share the same wheel speed sensors and actuator, so one bad input disables all of them at once.

Can new brake pads or rotors fix an ABS light?

Only indirectly. If worn pads let the fluid level drop, new pads plus a correct fluid level can clear it. If a sensor wire was damaged during a brake job, the wire is the fix, not the parts.

Will disconnecting the battery clear the ABS light?

It may clear it briefly, but if the fault is still there the module will find it again, usually within the first few miles. Fix the cause, then clear codes with a scan tool.

Is there an ABS recall for the 2002-2006 Q45?

NHTSA records show no ABS recall for these years. The 2004 model does have a brake lamp switch recall, so check your VIN.

Sources

1. Infiniti 2003 Q45 press kit - Q45 uses 4-wheel vented discs with 4-wheel ABS, EBD and Brake Assist; VDC standard on every Q45
2. NHTSA recall data, 2004 Infiniti Q45 - 2004 Q45 recall 04V497000 (brake lamp switch) and 12V079000 (side air bag connector); no ABS recall listed
3. NHTSA recall data, 2002 Infiniti Q45 - 2002 Q45 recall list contains no brake or ABS campaign
4. INFINITI ABS actuator safety recall notice - The ABS actuator leak recall covers certain 2017 QX60 vehicles, not the Q45
5. Brake and Front End: Wheel Speed Sensors - Debris on sensor tips, tone ring damage and air gap cause weak signals; confirm the code source before replacing a sensor
6. AA1Car: Diagnosing ABS Wheel Speed Sensors - Sensor faults disable ABS and light the warning lamp; AC output and scope testing methods