1990-1992 Infiniti Q45 ABS Module: Diagnosis, Compatibility, and Common Failures

Symptoms of a Failing 1990-1992 Q45 ABS Module

When the ABS control module in an early Q45 begins to fail, the signs are usually very clear. Because this is a pre-OBD-II vehicle, the symptoms are your primary diagnostic tool.

• ABS Warning Light: The most common symptom is an illuminated amber "ABS" warning light on the instrument cluster. This light indicates that the ABS computer has detected a fault in the system and has shut itself down.
• Wheels Locking Up: During hard or emergency braking, you may feel one or more wheels lock up and skid. This happens because the module is not intervening to modulate brake pressure, causing the car to behave like a vehicle without ABS. This is especially dangerous on wet or slippery roads.
• Unresponsive or Hard Brake Pedal: In some cases, a failing module can affect the feel of the brake pedal, making it feel unusually hard or unresponsive.
• Noises from the ABS Pump: You might hear the ABS pump motor running constantly, or not engaging at all when it should during a self-test at startup.

Diagnosing the Problem: Reading Blink Codes

The 1990-1992 Infiniti Q45 uses a pre-OBD-II diagnostic system. You cannot use a modern OBD-II scanner to read codes from the ABS module. Instead, you must retrieve "blink codes" by manually accessing the system's self-diagnostics.

1. Locate the Diagnostic Connector: The diagnostic port on these early models is typically a grey, multi-pin connector found in the driver's or passenger's footwell, often near the fuse box. It is NOT the standardized 16-pin port found on 1996 and newer vehicles.
2. Ground the Diagnostic Pin: You will need a short piece of wire or a paperclip to connect a specific pin on the diagnostic connector to a chassis ground (any bare metal bolt or bracket). Forum posts for similar era Nissan/Infiniti vehicles suggest this is often Pin 4 or Pin 9.
3. Read the Flashes: Turn the ignition key to the 'ON' position without starting the engine. The ABS warning light on the dashboard will begin to flash in a sequence.
4. Interpret the Codes: The codes are two-digit numbers. The sequence will consist of long flashes (for the first digit) followed by short flashes (for the second digit). For example, two long flashes followed by three short flashes indicates code "23". Count the flashes carefully and write down the codes.
5. Look Up the Codes: Once you have the codes, you will need to reference an FSM to understand what they mean. Common codes relate to wheel speed sensor failures, pump motor circuit faults, or internal module errors.

Known Issues & Common Failure Modes

Internal Capacitor Failure

The most common cause of failure for this 30+ year-old electronic module is not physical damage, but the degradation of internal components. Like many Japanese electronics from the 1980s and 90s, these modules are susceptible to "capacitor plague."

The electrolytic capacitors on the circuit board eventually leak their acidic fluid. This corrosive electrolyte can eat away at the copper traces on the board, causing short circuits or open circuits. When inspecting a module, look for small, barrel-shaped components with any of the following signs:

• A fishy or rotten seafood smell coming from the module.
• Bulging or leaking tops.
• Dark, crusty residue around the base of the capacitors on the circuit board.

If you have experience with electronics repair and soldering, you can often fix the module by replacing these capacitors with new ones of the same rating. However, if the board itself is damaged, replacement is the only option.

Buying a Used ABS Control Module

Given that new OEM modules are no longer available, a quality used OEM module is the best solution. Here’s what to look for:

• Verify the Part Number: The only way to guarantee compatibility is to match the part number. You must have part number 47850-60U00.
• Confirm Vehicle Options: Double-check that the donor vehicle did not have Traction Control or HICAS. An honest seller should be able to provide this information.
• Physical Inspection: Ask the seller for clear photos of the module's exterior and connectors. Look for any signs of water damage, corrosion, or physical trauma. If possible, ask for a picture of the internal circuit board to check for signs of leaking capacitors or previous, low-quality repair work.
• Why Used OEM is Best: For a vintage vehicle like this, a used original part is far superior to any theoretical aftermarket equivalent. The OEM module was designed for the car's specific systems. There are no reliable new aftermarket options for this particular part.

Programming and Installation

Good news for DIY mechanics: this module requires NO programming or flashing. It is a simple plug-and-play unit.

1. Location: The ABS control module is located on the right-hand (passenger) side of the dashboard, positioned above the glove box.
2. Removal: You will need to remove the glove box assembly to gain access. This typically involves removing several screws and clips.
3. Installation: Once accessed, the module is held in by a few bolts and has one or two electrical connectors. Disconnect the battery, unplug the old module, unbolt it, and install the new one in the reverse order.

Cost of Replacement

Replacing the ABS module on a 1990-1992 Q45 is relatively affordable, especially when using a recycled OEM part.

Frequently Asked Questions (FAQ)