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- Squeaking, Squealing or Grinding Noises
- Soft or Spongy Pedal
- Vibration When Braking
- Brake Light Is Illuminated
- While Braking, Car Pulls to One Side
- Burning Smell
- Brake Fluid Leaks
Right now we’re offering a 15% Off Brake Special! (Through Dec 31, 2017). Please remind us of the discount at the time of write up.
I’ve written more about OBD II readiness monitors than any other subject that I’ve covered at JustSmogs.com. Unfortunately, I don’t think that I’ve done a very good job explaining what they are.
…If the monitor on my car is the problem, how much does it usually cost to get a replacement monitor?
Comment from a reader in response to:
Smog Check OBD II (OBD 2): What are Readiness Monitors?
An OBD II readiness monitor is not something that you can see, touch, smell or taste. You can not repair or replace an OBD II readiness monitor.
If you were told that your vehicle did not pass a smog inspection because your car’s OBD II readiness monitors were not complete, it doesn’t mean that you have a bad monitor.
OBD II readiness monitors are not sensors!
Your car has an engine control module (Computer). That computer is loaded with software that performs many functions. Some of those functions, or processes, are referred to as OBD II readiness monitors.
OBD II readiness monitors are software processes that monitor (Test) critical emissions control systems.
These processes (Monitors) are referred to by name of the system(s) that they monitor (Test).
Comprehensive Component (Shorts, opens, other electrical issues)
Heated Catalyst (Uncommon)
O2 Sensor Heater
Secondary Air Injection
Not all of the above monitors will be programmed into every vehicle. For example, there will be no Secondary Air Injection monitor on a vehicle that is not equipped with a secondary air injection system because there is no secondary air injection system to monitor (test) on that vehicle.
Again, OBD II readiness monitors are tests run by your vehicle’s computer software. OBD II readiness monitors are not physical components or sensors.
…So if you have a ford or chevy with 9 monitors, 8 have to be ready if you have a brand new german car with 100 sensors, 99 have to be ready – how stupid is that….. “1 not ready” is a stupid criteria. My old ’95 only had 2 sensors – so “none” ready would have passed…
Excerpt from a forum post at
The author of that post is a confused about OBD II monitors, but that’s OK, so are many automotive professionals.
Also, there is not a 1:1 ratio between monitors and sensors. Even if a gasoline powered vehicle is equipped with “100 sensors”, It will have no more OBD II readiness monitors than those listed above.
When your car’s computer detects a problem that could cause an increase in harmful emissions (Smog), it will set a diagnostic trouble code (DTC) and turn on the “Check Engine Light”.
The check engine light is also known as the Malfunction Indicator Light (MIL), Service Engine Soon, and the funny looking thing with the lightning bolt going through it).
The computer identifies problems by running the diagnostic tests that we call monitors.
If no diagnostic trouble codes are stored in memory and all OBD II readiness monitors are complete, it is safe to assume that the vehicle’s emissions control systems are working properly; however, if the monitors are incomplete, there might be a problem with the emissions control system that has not been identified.
Since OBD II testing and system health is a major component of today’s smog inspection, a vehicle can not pass a smog inspection unless all systems are ready.
If they’re not broke, then why aren’t my monitors ready?
By design, OBD II monitors are composed by tests that run in the background and the average motorists never has to give OBD readiness monitors a second thought.
OBD readiness monitors are normally “Ready” (Complete). If OBD II monitors are “Not Ready” (Incomplete), it is usually because of one of the following reasons:
The computer lost power
The results of tests run by OBD II readiness monitors are stored in what is known as volatile memory.
Volatile memory, contrary to non-volatile memory, is computer memory that requires power to maintain the stored information; it retains its contents while powered on but when the power is interrupted, the stored data is lost immediately or very rapidly.
Reasons for a vehicle’s computer to loose power commonly include:
- A dead or depleted battery.
- A battery that has been disconnected.
- Electrical problems that could include blown fuses and damaged wiring.
One of my customers had an ignition interlock device installed on her vehicle after she plead guilty to a DUI. The device installed on her vehicle worked by interrupting the power supply to her car’s computer.
Because of that interlock device, the OBD II readiness monitors on her car were cleared every time she turned switched off the ignition on her car.
When power returns to the computer all monitors will indicate a “Not Ready” or “Incomplete” state (The term used will depend on the diagnostic scan tool used to check monitors).
Cleared with a diagnostic scan tool
In some cases the check engine light may be cleared as part of the diagnostic process. A technician might gather relevant information, and then verify that the problem still exists by clearing the code and confirming that the code returns under similar conditions.
In any case, the check engine light is usually cleared following the completion of repairs.
By design, when codes are cleared using a diagnostic scan tool or code reader, OBD readiness monitors are also cleared.
Most shops will instruct their customer to drive the car normally, and return to the shop only if the original symptoms, including the illuminated check engine light, return. In most cases this isn’t a problem, but what if the customer leaves the repair shop and drives straight to a smog shop? That customer might have a problem.
So, what do I have to do to get my monitors ready?
Drive your car!
I won’t begin to describe some of the silly and outright dangerous schemes that people come up with to avoid driving their own cars.
Each monitor (Test) has a specific set of conditions (Enabling criteria) that must be met before that monitor can be run to completion.
The best way to complete readiness monitors, especially on car that is having trouble completing those monitors, is to obtain a copy of the manufacturer’s suggested drive cycle. In most cases, that drive cycle is only an internet search away.
I can’t do that in Los Angeles/Orange County traffic!
At Just Smogs® in Huntington Beach, we frequently perform OBD II readiness drive cycles for our customers during normal business hours.
Earlier this month, a customer from Temecula brought us a Jeep with “impossible to run monitors”. After allowing the Jeep to fully cool down, one of my team members warmed up the Jeep and took it out for a spin. He was back in less than an hour. All monitors were complete.
Here are some tips for running monitors and difficult vehicles:
- Follow all manufacturer instructions, not just the ones you like. Deviating from the drive cycle instructions briefly can take you back to square one.
- I often recommend running monitors early on a Saturday or Sunday morning when traffic is usually light. Also, some monitors will not complete during extremely hot or cold weather (Usually the EVAP monitor).
- In most cases, allow the vehicle to cool down completely overnight. It’s usually important to perform a complete warm up cycle before beginning the drive cycle. Allow the vehicle to warm up naturally while idling. Unless the drive cycle instructions indicate otherwise, avoid revving the engine in an effort to warm it up quickly.
- Once again, follow the manufacturer’s instructions completely!
I’ve done all that, and they still wont run!
There are times when the drive cycle will not work!
Normally a problem with a monitored system, sensor, or other component, will trigger a diagnostic trouble code and the computer will turn on the check engine light.
However, sometimes an under-performing system that is on the verge of failure will prevent the completion of a test, but not trigger a diagnostic trouble code.
For example an under-performing oxygen sensor might prevent the completion of a catalyst monitor, or an exhaust leak might affect an oxygen sensor’s performance just enough that it prevents the monitor from running to completion. Even though the check engine light might be off, a monitor might not complete until necessary repairs are performed.
Some vehicles have known software or hardware issues that prevent monitors from being run to completion. In those cases the vehicles computer may require reprogramming or replacement. The vehicle may even be subject to a manufacturer recall.
More information about OBD II monitors and problem vehicles can be found in the OBD II Smog Check OBD Reference maintained by the California Bureau of Automotive Repair.
Just Smogs® in Huntington Beach specializes in the diagnosis and repair of emissions related issues including OBD II monitor issues. For information about diagnostics, repair, or the Just Smogs® monitor drive cycle service, call Just Smogs® at (714) 596-1019.
We are eternally grateful to our fellow Americans who have made the ultimate sacrifice to preserve our freedom and way of life. We owe their families a debt that we can never repay.
A reader wrote in to say that she’s having trouble getting her 2007 Volkswagen Rabbit to complete OBD II monitors. I shared the following drive cycle wither her, and decided to post it here for others experiencing similar issues with their Volkswagen vehicles.
This drive cycle should be valid for Volkswagen engine codes BGP and BGQ.
- Switch the ignition on and start the vehicle.
- Idle the vehicle for 2-3 minutes. This executes the O2S Heater, Misfire, Secondary AIR, Fuel Trim, and Purge system monitors.
- Drive the vehicle at 45-55 mph for a continuous 7 minute period, avoid stopping. This executes the EVAP, O2S, Fuel Trim, and Misfire monitors.
- Accelerate the vehicle to an engine speed of 5000 RPM (with automatic transmission use the tip-tronic mode) lift off the throttle until the engine speed is around 1200 rpm. This executes the fuel cut off
- Accelerate the vehicle smoothly to 60-65 mph, cruise constantly for 5 min, this executes the Catalyst, O2S, Misfire, Fuel Trim, and Purge System monitors.
- Decelerate and idle the vehicle again for 3 minutes. This executes the Misfire, Secondary AIR, Fuel Trim, and Purge system monitors.
As with most OBD II monitor drive cycles, a complete warm-up cycle is recommended. In other words, let the vehicle cool down completely and allow the vehicle to warm up to full operating temperature from a cold start before commencing the drive cycle. Also, it might be necessary to perform the drive cycle on a weekend morning when traffic is light.
Drive safely and observe all traffic laws while performing the drive cycle. Several attempts may be required. Rinse and repeat as necessary.
Evaporative Emissions Control System (EVAP)
What Does The EVAP System Do?
The evaporative emissions control system (EVAP) on your vehicle is designed to prevent fuel vapors from escaping into the atmosphere from your gasoline tank.
Fuel vapors are composed of hydrocarbon molecules (HC) which when exposed to sunlight and oxides of nitrogen (NOx) result in photo-chemical smog. Photo chemical smog is that brown hazy stuff that nobody wants to see in the sky.
These compounds are also known to cause eye irritations and respiratory problems. That’s why hydrocarbon control and reduction is a major component of your car’s emissions control strategy.
How Does The EVAP System Work?
When your engine is running and warmed up, engine vacuum siphons stored fuel vapors from the EVAP canister and into the intake manifold. These fuel vapors are added to the engine’s air fuel mixture and are burned off as part of the normal combustion process.
EVAP And The Check Engine Light
When many people see a “Check Engine Light” (Proper name: Malfunction Indicator Light ; a.k.a MIL) they immediately think, “Check the gas cap”. That’s because a missing, loose, or damaged gas cap often is the cause of an illuminated MIL due to a failed EVAP leak test.
During EVAP testing, a loose or missing gas cap will be detected as a leak, a diagnostic trouble code will be stored, and the MIL will illuminate.
A loose gas cap might result in a P0442 code, (Small leak detected), and a missing cap could return a P0455 (Large leak detected).
Loose and missing gas caps are not the only cause of EVAP system leaks, but they are the number one suspect.
The information presented below is an example of diagnostic strategies that a technician might employ while diagnosing your vehicle’s EVAP system. It is not intended to be exhaustive, complete, or even applicable to all situations. Always follow a vehicle manufacturer’s procedures when performing tests or repairs of any kind.
EVAP related diagnostic trouble codes that turn on your check engine light can be set for a variety of reasons. Some faults are caused by leaks while others can result from blocked lines, faulty sensors, or malfunctioning solenoids.
Some vehicles have had issues with spiders laying eggs in EVAP vent lines while others have problems as simple as corrosion preventing a good seal between the fuel cap and fuel filler neck. There’s more to look out for than bad gas caps.
That’s why its important for you to have your vehicle diagnosed at a shop that employs technicians with the skills, training, and equipment necessary to correctly diagnose and repair your vehicle without wasting your time and money on unnecessary repairs and hopeful guesses.
Before reaching for high tech solutions, a technician should review the basics.
You should be asked questions about your vehicle.
“Have you had any work done on the car?”.
To which you might reply:
“Oh yeah, me and my brother had to drop the gas tank and replace the fuel pump. We had a lot of trouble with one of the seals. It got a little chewed up, but my brother said it would be fine”.
A little information goes a long way towards finding the solution to a problem.
Technical Service Bulletins
The technician diagnosing your vehicle should also look for EVAP related Technical Service Bulletins (TSBs). Are there any known issues with the vehicle that could explain the presence of the diagnostic trouble code.
There was an issue with my wife’s 2005 Toyota Corolla that caused several false EVAP diagnostic codes to set.
Before doing anything else, I checked for recalls and technical service bulletins. It didn’t take me long to find out that Toyota had issued a recall, and her Corolla was one of the affected vehicles.
An ECM manufacturing flaw was causing false EVAP codes to set. A few minutes of research saved me from a few weeks of pulling my hair out trying to find the problem.
When I asked my wife, she said that she received the recall letter, but didn’t think that it was important because the “car drove fine”.
Knowledge About The System Being Diagnosed
EVAP control strategies vary from manufacturer, model, and model year. Understanding a system and how it works is the essential first step towards identifying a problem with a system when it doesn’t work according to design.
The Five Senses
A technician will look for loose, missing, or damaged components.
We will often wiggle wires and hoses while looking, listening, and even sniffing for changes.
We’ll remove the gas cap and look for damage to the gas cap, o-ring, and filler neck. While reinstalling the gas cap we’ll pay close attention to how it fits. Sometimes an incorrect gas cap will look right, but it will not fit right. We’ll listen for clicks. Does it sound like the cap “locked”?
We’ll use our sense of smell. The presence of a strong fuel odor, especially during low pressure fuel EVAP testing, is often the first indication that the EVAP system has been compromised
We’ll look again. Is there a puddle of gasoline under the vehicle? Clearly the EVAP system will not seal if there is a large hole in the gas tank.
Smoke testing is a common and effective way to pinpoint the location of leaks in a vehicle’s evaporative emissions control system.
While smoke testing for leaks, the EVAP system should be sealed. The purge valve is normally closed, but a technician will usually need to command the EVAP system’s vent valve closed using a scan tool.
I like to start by test the EVAP system with all components in place. If possible, I’ll introduce smoke through the EVAP system’s test port. The EVAP test port is schrader valve often located in the engine compartment of a vehicle and easily recognized by a green cap.
I’ll then look for smoke leaking from valves, EVAP lines, around the fuel cap, the fuel filler neck, and around the gas tank.
If I see smoke I’ve found a leak (Not necessarily all leaks). Once the leak has been repaired, I’ll repeat the test and ensure that there are no other leaks.
If no smoke is seen on the initial test, I’ll introduce smoke from the fuel filler neck. I’ll then look leaks at, or near, the fuel the test port that may have missed when with the smoke tester was attached.
If I still do not see smoke, I’ll reconnect the smoke machine to the EVAP test port and start testing the valves themselves for leaks. For example, I might disconnect the hose on the canister side of the purge valve. Since the purge valve is normally closed, any smoke exiting the purge valve at this stage would be a pretty good indication of a leak.
The same is true for smoke exiting a vent valve that has been commanded closed. The valve might be leaking, or there could be a problem on the command side of the circuit (Perhaps a bad ground is preventing activation of the valve), or the valve may have failed electrically. By testing the circuit and the component I can quickly identify the point of failure.
I’ll also disconnect electrical connectors while smoking the system. We recently had a Dodge Caravan in the shop that showed no sign of a leak until we disconnected the electrical connector at the leak detection pump (Kind of ironic isn’t it), suddenly smoke started pouring out of the connector. With the harness in place there was no sign of a leak.
Look, I’ve tested this car every possible way, and there is no leak!
A diagnostic trouble code indicating an EVAP leak is only as reliable as the system that triggered it.
For example: A faulty fuel tank pressure sensor might cause the on-board diagnostic system to falsely indicate a leak.
It’s possible to test the fuel tank pressure sensor without removing parts.
Any shop performing EVAP diagnostics and repairs should have a scan tool (Preferably bi-directional), and at least one of the following:
A Smoke Machine
A Low Pressure Fuel Evap Tester (LPFET)
First, I’ll connect the scan tool to the vehicle’s diagnostic link connector (DLC) and observe the Fuel Tank Pressure Sensor parameter.
The next step is to safely change the pressure in the fuel tank. After noting the Fuel Tank Pressure Sensor value, I connect my smoke machine, or my LPFET, to the fuel filler neck. make sure you have a good seal. (Again, be sure to observe all manufacturer warnings and procedures. Refer to your equipment manufacturer’s documentation to determine the amount of pressure your tool will add to the tank.)
Again, I’ll observe the Fuel Tank Pressure Sensor value on my scan tool. I should observe an increase in pressure as compared to the original reading. If the value does not change, or does not increase according to the amount of pressure applied by my equipment, and I have verified that the EVAP system is sealed, I’ll suspect a faulty Fuel Tank Pressure Sensor.
This is just one example how direct observation and an understanding of how a vehicle’s EVAP system works can help diagnose a sensor problem after an EVAP system leak has been ruled out.
As OBD II diagnostics and EVAP emissions control strategies become more complex and sophisticated, EVAP diagnostics and repairs are a frequent challenge faced by technicians in the field.
When diagnosing EVAP system related diagnostic trouble codes, as with most codes, its important to remember that diagnostic trouble codes are merely a starting point for diagnosis, and not the solution.
A technician should observe the basics, do his homework, and understand how to use the tools at his disposal.
If you’re in Huntington Beach, Fountain Valley, Long Beach, or the surrounding areas and your vehicle has failed a smog inspection because of an EVAP related problem, you can roll the dice with one of those other guys and hope they know the difference between P0442 and a P0443, or you could call the ASE certified professionals at Just Smogs® in Huntington Beach and have your car diagnosed by a team that has the knowledge, training, and skill to do more than just throw parts at a problem.
Call Just Smogs today at (714) 596-1019, or you could try going at it yourself, but who wants to deal with spiders in the vent line?