P0959

ASM Mode Circuit Intermittent

Powertrain Chassis/Safety Anti-lock Braking System 🟡 Moderate — Fix within a week ⚠️ Drive with Care
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What This Actually Means

In plain language — no jargon

Your engine's anti-lock braking system (ABS) control circuit is losing connection intermittently, like a loose phone charger that only works when held at the right angle. The ECU detects electrical signals dropping in and out when they should stay steady.

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Symptoms You May Notice

3 known symptoms for this code
ABS warning light flashing or staying on intermittently
Loss of ABS function during braking cycles
Traction control warning light illuminating
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors the voltage and signal continuity of the ASM (Anti-lock System Module) circuit during operation. It expects consistent electrical presence and valid data handshakes; intermittent dropouts or voltage spikes trigger this fault. The issue is typically a loose connector, corroded pin, or failing wiring that causes sporadic signal loss.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
ASM Circuit Voltage 12-14.5V steady state Voltage drops below 10V or signal loss detected
Signal Continuity Continuous valid communication Intermittent signal dropout or CAN bus errors
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
ABS module connectors and pins
Inspect and reseat all ABS module connectors under the wheel wells and engine bay, cleaning any corrosion with contact cleaner.
2
ABS wiring harness
Check for damaged, pinched, or corroded wiring between the ABS module and wheel speed sensors; repair or replace damaged sections.
3
ABS module relay or fuse
Test and replace the ABS control module relay or fuse if it shows signs of burning or poor contact.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P0959 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code P0959

What happens after you fix the fault

Once the fault is repaired, P0959 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.