Getting your Audi through a smog test can sometimes feel like navigating a complex maze. If you’re facing a stubborn “CAT” monitor that’s not setting to “ready,” you might be exploring the Audi Drive Cycle. This procedure is designed to help your car’s onboard diagnostic system (OBD-II) run specific tests and confirm that all emission systems are functioning correctly. Let’s break down the Audi drive cycle, understand its steps, and how to use it effectively to ensure your vehicle passes its emissions test.
The drive cycle is essentially a pre-programmed series of driving maneuvers that simulate typical driving conditions. For Audi vehicles, like your 2004 A4 Quattro 3.0L, following this cycle is crucial for resetting emission monitors. These monitors, including the Catalyst (CAT) monitor, are self-tests that your car performs to ensure its emissions control systems are working as they should. If these monitors haven’t completed their tests – often indicated as “not ready” – your vehicle will fail a smog test, even if there isn’t an obvious problem.
Here’s a detailed breakdown of the Audi drive cycle stages, as outlined in official documentation, to help you understand each step and its purpose:
Step-by-Step Audi Drive Cycle Procedure for Your Audi
This sequence is designed to activate various emissions monitors in your Audi’s system. It’s important to follow these steps in order and as precisely as possible for the drive cycle to be effective.
Stage 1: Cold Start
The drive cycle begins with a cold start. This is critical because many emissions tests are initiated only when the engine is cold. For your Audi to register a cold start, certain conditions must be met:
- Engine Coolant Temperature: Must be below 122°F (50°C).
- Temperature Proximity: The engine coolant temperature and intake air temperature should be within 11°F (6°C) of each other at startup.
This ensures the engine control module (ECM) recognizes a true cold start and initiates the necessary monitor checks.
Stage 2: Idle for 2 Minutes
After the cold start, allow your Audi to idle for two minutes. During this period, it’s recommended to turn on the air conditioning (A/C) and headlights. This might seem counterintuitive, but adding electrical load helps to stabilize combustion and assist the misfire monitor in running effectively. This idle stage is crucial for activating several monitors:
- O2S Heater Monitor: Checks the functionality of the oxygen sensor heaters.
- Secondary Air Injection (AIR) Monitor: Tests the secondary air injection system.
- Evaporative Emission System (EVAP) Monitor: Starts the process of checking the EVAP system for leaks.
- Misfire Monitor: Assesses engine misfires.
- Fuel System Monitor: May run if the system is operating in closed loop.
Image showing a car idling, representing Stage 2 of the Audi drive cycle focusing on the idle period for emissions monitor activation.
Stage 3: Accelerate to 55 MPH
Before accelerating, turn off the A/C and headlights to reduce load on the engine during acceleration. Accelerate smoothly and steadily to 55 MPH (89 KPH), opening the throttle to about halfway. This acceleration phase is important for engaging:
- Misfire Monitor: Continues to monitor for engine misfires under load.
- Fuel System Monitor: Further evaluates the fuel delivery and control system.
- EVAP Monitor: Continues testing the evaporative emissions system.
Stage 4: Steady State Cruise at 55 MPH
Maintain a steady cruise at 55 MPH (89 KPH) for a specific duration (often around a few minutes, though the original document doesn’t specify the time for this stage). This constant speed cruise is vital for running several monitors:
- Oxygen Sensor (O2S) Monitor: Evaluates the performance of the oxygen sensors.
- Secondary Air Injection (AIR) Monitor: Continues testing the AIR system.
- Exhaust Gas Recirculation (EGR) Monitor: Tests the EGR system’s functionality.
- EVAP Monitor: Continues its leak detection and system check.
- Misfire Monitor: Monitors misfires during steady cruise.
- Fuel System Monitor: Checks fuel system performance under cruise conditions.
Stage 5: Decelerate
Gradually decelerate from 55 MPH without applying the brakes. For manual transmission vehicles, keep the car in high gear and do not press the clutch. This coast-down period is important for:
- EGR Monitor: Tests the EGR system during deceleration.
- EVAP Monitor: Continues monitoring the EVAP system.
- Fuel System Monitor: Checks fuel system behavior during deceleration.
Stage 6: Accelerate to 60 MPH
Accelerate again, this time reaching 60 MPH (97 KPH). Apply throttle smoothly until you reach this speed. Similar to the previous acceleration phase, this step helps to run:
- Misfire Monitor: Checks for misfires under acceleration.
- Fuel System Monitor: Evaluates fuel system performance during acceleration.
- EVAP Monitor: Continues EVAP system testing.
Stage 7: Steady State Cruise at 60 MPH for 5 Minutes (Catalyst Monitor Focus)
Maintain a steady cruise at 60 MPH (97 KPH) for 5 minutes. This stage is explicitly mentioned in the original query as being related to the CAT monitor. This extended cruise at a slightly higher speed is critical for evaluating the efficiency of your catalytic converter and other emission components:
- Catalyst (CAT) Monitor: This is the primary monitor targeted in this stage, assessing the catalytic converter’s ability to reduce emissions.
- Oxygen Sensor (O2S) Monitor: Further evaluation of oxygen sensor performance.
- Secondary Air Injection (AIR) Monitor: Continues testing of the AIR system.
- EGR Monitor: Continues EGR system checks.
- EVAP Monitor: Ongoing EVAP system monitoring.
- Misfire Monitor: Misfire detection during cruise.
- Fuel System Monitor: Fuel system performance check during cruise.
Image illustrating a car cruising on a highway, representing Stage 7 of the Audi drive cycle, crucial for catalyst monitor assessment during a steady state cruise.
Stage 8: Decelerate (Final Coast Down)
Gradually decelerate again from 60 MPH without using the brakes. As in Stage 5, for manual transmissions, keep the vehicle in high gear and do not depress the clutch. This final deceleration phase allows for:
- EGR Monitor: Final checks of the EGR system.
- EVAP Monitor: Concluding tests for the EVAP system.
- Fuel System Monitor: End-of-cycle fuel system evaluation.
Can You Just Do Stage 7 for the CAT Monitor?
The original post asks if Stage 7, the 5-minute cruise at 60 MPH, can be performed in isolation to specifically address the CAT monitor. While Stage 7 is indeed heavily focused on the catalyst monitor, it’s generally not recommended to skip the preceding stages.
The entire drive cycle is designed as a sequence. Each stage prepares the system for the next, and various monitors are initiated and run throughout the entire process. Skipping earlier stages might mean that the conditions necessary for the CAT monitor to run effectively in Stage 7 are not fully met.
However, if you are pressed for time or have repeatedly run the full drive cycle without success, attempting Stage 7 in isolation might sometimes work. The note in the original document mentions:
NOTE: If the CAT is marginal and the battery was disconnected prior to the Drive Cycle, it may take up to five separate Drive Cycles in order to determine the state of the CAT.
This suggests that for a marginal catalytic converter, or if the battery was recently disconnected (which resets the monitors), multiple attempts at the drive cycle, particularly the CAT-focused Stage 7, might be necessary.
Therefore, while not ideal, you could try repeating Stage 7 multiple times. Ensure you are performing it correctly – maintaining a steady 60 MPH for 5 minutes – and allow some cool-down time between attempts. However, if this doesn’t work after a few tries, it’s best to perform the complete drive cycle from Stage 1 to Stage 8.
Tips for a Successful Audi Drive Cycle
- Follow the Steps Precisely: Adhere to the speed and duration guidelines for each stage as closely as possible.
- Start with a Cold Engine: Ensure a genuine cold start as described in Stage 1.
- Safe Driving Conditions: Perform the drive cycle in a safe location where you can legally and safely perform the accelerations and steady-state cruises. Avoid heavy traffic areas.
- Avoid Abrupt Stops and Starts: Drive smoothly and avoid sudden braking or acceleration unless specified in the drive cycle.
- Check for Trouble Codes: Before starting the drive cycle, use an OBD-II scanner to check for any Diagnostic Trouble Codes (DTCs). Address any codes present, as they can prevent monitors from setting to “ready.”
- Battery Condition: Ensure your car battery is in good condition. A weak battery can sometimes interfere with monitor operation.
- Multiple Attempts May Be Needed: As the note indicates, especially for the CAT monitor, you might need to perform the drive cycle multiple times, up to five or more, to get the monitor to set.
Conclusion
Mastering the Audi drive cycle is a valuable skill for any Audi owner, particularly when facing smog test requirements. By understanding each stage and following the procedure diligently, you increase your chances of setting all emission monitors to “ready,” including the often-stubborn CAT monitor. While focusing on Stage 7 alone might offer a shortcut in some cases, performing the complete drive cycle is the most reliable approach. If you continue to experience issues after multiple attempts, it’s advisable to consult a qualified automotive technician to diagnose any underlying problems with your vehicle’s emission system.
