Permanent Diagnostic Trouble Codes

What are Permanent Diagnostic Trouble Codes?

Permanent Diagnostic Trouble Codes (PDTCs) are very similar to regular Diagnostic Trouble Codes (DTCs). However, unlike regular DTCs, they cannot be reset by disconnecting the vehicle’s battery or cleared using an On-Board Diagnostic (OBD) scan tool. The only way to clear a PDTC is to fix the underlying problem with the vehicle that originally caused the PDTC and its corresponding DTC to set, and then allow the vehicle sufficient drive time to re-run the monitor that identified the problem in the first place. When the monitor runs without identifying a problem, the PDTC will clear itself.

When will PDTCs be included as part of the Smog Check inspection failure criteria?

Starting July 1, 2019, the presence of PDTCs will be considered in determining the vehicle’s Smog Check inspection result.

Why are PDTCs being included in the Smog Check Program?

Unplugging the vehicle’s battery or using a scan tool are techniques sometimes used to clear OBD information for a vehicle that has an illuminated malfunction indicator light in an attempt to hide the fact that the vehicle is malfunctioning. Some of these vehicles can pass a Smog Check inspection before the vehicle can re-identify the underlying problem that set the malfunction indicator light and DTC(s). This can have a dramatic impact on air quality and decrease the effectiveness of the Smog Check Program. Although the use of readiness monitors reduces the chances of passing a Smog Check inspection with an active DTC, PDTCs can further ensure emission control systems are working correctly.

How are PDTCs going to be used as part of a Smog Check inspection?

Upon implementation, vehicles that have a PDTC stored in the OBD system will fail the Smog Check inspection regardless of whether the malfunction indicator light is illuminated. If a PDTC is stored, it indicates that the OBD system has not yet successfully verified that a previously detected emissions-related malfunction is no longer active.

Which model-year vehicles will include PDTCs as part of the Smog Check inspection?

The new criteria will apply to model-year 2010 and newer vehicles that support PDTCs.

What if the vehicle does not properly support PDTC functionality?

BAR is working with the Air Resources Board (ARB) to ensure that known problematic vehicles are addressed by the vehicle manufacturers. In the meantime, BAR will control application of such vehicles through the Smog Check database, and list them in the Smog Check OBD Reference. Vehicles that do not support PDTC storage will not be subject to this part of the Smog Check inspection.

What is the estimated increase in Smog Check inspection failure rate for the inclusion of PDTCs?

BAR analysis indicates the new requirement could initially increase Smog Check inspection failure rates by less than half a percent (0.2 to 0.3%).

Are there circumstances under which a PDTC will not cause a vehicle to fail a Smog Check inspection?

Yes. PDTCs will be ignored if the vehicle has completed at least 15 warm-up cycles and been driven at least 200 miles since its OBD information was last cleared.

Why will PDTCs be ignored when the vehicle has completed 15 warm-up cycles and been driven 200 miles since the codes were cleared?

The time to complete 15 warm-up cycles and drive 200 miles is reasonable for vehicles to complete the self-diagnostic tests. In fact, most vehicles will complete the self-diagnostic tests well before this maximum limit is reached. The 15/200 limit is being established to prevent undue inconvenience to motorists who are trying to comply with the Smog Check Program requirements but are having trouble getting specific monitors to run to completion and ready for testing.

Is there financial help available to consumers whose vehicles fail Smog Check for a PDTC?

The Consumer Assistance Program (CAP) offers both repair assistance and vehicle retirement options to eligible consumers. Income-eligible consumers may receive financial assistance with emissions-related repairs if their vehicle fails a biennial Smog Check inspection. Consumers who meet eligibility requirements may receive up to $1,500 to retire their vehicle.

Above information is courtesy of

Confusion About OBD II Monitors

I’ve written more about OBD II readiness monitors than any other subject that I’ve covered at 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?

Is an OBD II monitor bigger than a breadbox?

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).

Just Smogs® 7722 Talbert Ave, Huntington Beach, CA

Fuel Management


Comprehensive Component (Shorts, opens, other electrical issues)


Heated Catalyst (Uncommon)

O2 Sensor

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.

Why are OBD II Readiness Monitors Important?

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.

That means that if the computer in your vehicle looses power for any reason, the results of tests run by the computer’s OBD II readiness monitors will be cleared (erased, deleted, etc).

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

When a car comes into a shop with an illuminated check engine light (MIL), the vehicle should be properly diagnosed and repaired.

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:

  1. Follow all manufacturer instructions, not just the ones you like.  Deviating from the drive cycle instructions briefly can take you back to square one.
  2. 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).
  3. 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.
  4. 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.


February 2017 California Smog Check FAQ

Smog Check Frequently Asked Questions for February 2017

How do I submit my smog test?

How do I determine what year a car needs a smog check?

Does my RV require a smog check in California?

Smog Check Frequently Asked Questions for January 2017

Why did my car fail for incomplete OBD II readiness monitors? I Thought the rule was that my 1996-2001 car could pass with two incomplete readiness monitors.

How do I submit my smog test?

You don’t need to “submit” your smog test. The results of your smog inspection were electronically transmitted and submitted to the State of California at the conclusion of the smog inspection.

How do I determine what year a car needs a smog check?

Gasoline, Flex, CNG, LNG, LPG Powered Vehicles

1976 to current model year vehicles are subject to smog inspection.

All 1976 and newer model year vehicles entering the State of California require a smog certification prior to initial registration

Change of ownership smog inspections are required after the fourth model year

For example:

A 2016 model year gasoline powered vehicle would be subject to change of ownership smog inspections beginning in 2020 (2016 + 4 = 2020).

Biennial (Every two years) smog inspections begin after the sixth model year.

For example:

A 2016 model year gasoline powered vehicle would be subject to biennial smog inspections beginning in 2022 (2016 + 6 = 2022).

A good rule of thumb is that even number model years are due for smog inspections on even numbered years. Odd numbered model years are due on odd number years.

For example:

This year (2017) we started performing biennial smog inspections 2011 model year vehicles.  We’re also inspecting 2009, 2007, 2005, 2003, 2001, 1999, etc.


The only difference between hybrid/gasoline powered vehicles is that hybrids become subject to smog inspections beginning with model year 2000 instead of 1976.


Diesel powered vehicles under 14,000 pounds GVWR become subject to biennial smog inspections beginning with the 1998 model year.

Unlike the vehicles described above, diesels do not have a four year change of ownership exemption, nor do diesels have a six year new vehicle exemption.

Fleetwood Jamboree Smog CheckDoes my RV require a smog check in California?

In most cases, the answer is yes.

If your your 1976 or newer motor home (RV) is gasoline powered, and more than four years old, it is subject to smog inspections in the state of California.

If your 1998 or newer motor home (RV) is diesel powered and has a GVWR of 14,000 pounds or less it is subject to smog inspections in the state of California.

Click here for more information about smog requirements by vehicle type.

Why did my car fail for incomplete OBD II readiness monitors. I Thought the rule was that my 1996-2001 car could pass with two incomplete readiness monitors.

check engine lightEmission test rules previously allowed for a car to pass the smog inspection with two incomplete readiness monitors; however the rules changed effective May 4, 2015.

Most 1996 – 1999 model year gasoline powered vehicles will fail the California smog inspection if two or more OBD II monitors are incomplete. Any one OBD 2 readiness monitor can be incomplete and a gasoline powered car will pass the smog inspection.

Most 2000 and newer gasoline powered vehicles are subject to stricter rules.  A 2000 or newer model year vehicle will fail the smog inspection if any monitor other than the EVAP monitor is incomplete.

Most 1998 – 2006 OBD II certified diesel powered vehicles will fail the smog inspection if any monitors are incomplete.  All OBD II monitors must be complete in order for a 1998 – 2006 model year OBD II certified diesel powered vehicle to pass the California state smog inspection.

Most 2007 and newer model year OBD II diesel powered vehicles can pass with two incomplete monitors.  If more than two monitors are incomplete the vehicle will fail the smog inspection.

Some vehicles are known to have difficulties completing OBD II monitors and may be subject to different rules. For more information see the Smog Check OBD Reference.

Smog Check Frequently Asked Questions for January 2017

How many readiness monitors have to be complete to pass smog?

What if I cannot get my smog test in California before it is due?

Can I go to another smog check station after failing?

The shop that failed my car also does repairs, can I go someplace else for repairs?

A relative gave me a car, do I need a smog inspection?

If my check engine light doesn’t turn on at all will I pass smog?

If you fail OBD II on a smog check, should your overall smog fail?

OBD II Monitor Drive Cycle Service

multiple-smog-check-fountain-valleyIn recent years the California Bureau of Automotive Repairs (BAR) and the California Air Resource Board (CARB) have increasingly shifted the emphasis of the California emissions program to on-board diagnostic trouble codes &  monitor readiness. This is especially true for 2000 and newer model year vehicles.

If you are having trouble completing OBD II readiness monitors on your 1996 or newer vehicle, the licensed professionals at Just Smogs® in Huntington Beach can help.

OBD II Monitor Recap

What are OBD II readiness monitors?

just-smog-check-fountain-valley-front-800x480The short answer is that OBD II readiness monitors are usually something that average motorists never have to worry about until they have a reason to worry.

OBD II readiness monitors are self tests run by a vehicle’s on board diagnostic system.  OBD II monitors have two states: ‘ready’ and ‘not ready’.  Some scanners and code readers may display ‘complete’ , ‘incomplete’ , comp, inc, etc.  It all comes down to whether or not a test has been run to completion.

When one of these test fails, the check engine light is illuminated; otherwise, a driver normally has no indication that OBD II readiness monitors exist.

So what’s the problem?


It’s not uncommon for OBD II readiness monitors to be reset following repairs.  This is especially true if the check engine light was on.

If a vehicle’s power train control module (PCM – ‘The Computer’) loses power due to a dead or depleted battery, or if diagnostic trouble codes are cleared using a scan tool, all readiness monitors are automatically set to incomplete/not ready.

Incomplete readiness monitors aren’t  something that you have to worry about unless your vehicle is due for a smog inspection.

Readiness monitors are run in the background and by design do not affect driveability, safety, or fuel economy, but they are an important part of the California smog inspection program.

In order for a vehicle to pass a smog inspection in the state of California, most OBD 2 monitors must be run to completion.  For example, in order for most 2000 and newer gasoline powered vehicles to pass the smog inspection all monitors with the exception of the evap monitor must be complete.  If any monitor other than the evap monitor is incomplete the vehicle will fail the smog inspection.

If you’ve ever had an issue with OBD II readiness monitors, you’ve probably heard the phrase, “Drive it fifty to one-hundred miles and you should be fine”.

I drove my car hundreds of miles, and it still isn’t ready!

Some cars are known to have issues that can make completing OBD II readiness monitors extremely

BAR maintains a list of such vehicles and possible solutions (The Smog Check OBD II Reference).

Very often the solution involves following a very specific drive pattern that some motorists find difficult to complete during their normal driving routine.  That’s when Just Smogs® can help.

Just Smogs® OBD II Drive Cycle Service

huntington-beach-smog-store-frontIf your vehicle is otherwise in good repair, and you are having difficulties completing the OBD II drive cycle, the professionals at Just Smogs® can complete the drive cycle on most vehicles that do not require further repair or diagnosis.

This service offering does not include any diagnostics or repairs that may be necessary to enable the OBD II drive cycle, nor does it include diagnostics or repairs that may become necessary should the drive cycle trigger a diagnostic trouble code or check engine light.

Of course in most cases you should be able to complete the drive cycle yourself with no more effort than a Sunday drive, but in case you can’t, the professionals at Just Smogs® are here to help.

For more information about Just Smogs® OBD II drive cycle service, call (714) 596-1019.


BMW OBD II Communication and Monitor Issues

As touched upon in a previous post (Smog Check OBD Reference Update) certain 1999 and 2000 model year BMW vehicles with 2.5 liter and 2.8 liter displacement engines that are having trouble passing the smog inspection due to incomplete monitors may be subject to a voluntary emissions recall (00E-A01: Fault Access/O2 Readiness Codes).

Model Manufactured
E39 528i, 528iA, 528iT, 528iAT 2/99-7/99
E46 328i, 328iA, 323i, 323iA 3/98-7/99
E46 328iC, 328iCA, 323iC, 323iCA 2/99-7/99
E36/7 Z3 coupe 2.8 4/99-7/99
E36/7 Z3 roadster 2.8 4/99-7/99
E36/7 Z3 roadster 2.3 9/98-7/99

bmw-logoBMW has determined that certain 1999 & 2000 model year BMW automobiles with 2.5 liter and 2.8 liter displacement engines may not fully meet Federal Environmental Protection Agency (EPA)  and California Air Resources Board on-board diagnostic requirements.

There are two issues:

  1. Due to an engine control module software error, a communication conflict exists between the engine control module (“The Computer”) and the transmission control module (“The other Computer”).  This may lead to difficulties or prevent communication and data transmission between the engine control module and and diagnostic equipment (Including the “Smog Machine”).
  2. The oxygen sensor readiness monitor may not run to completion on affected E36/7, E46 and E39 vehicles.

Owners of affected vehicles should have received a letter from BMW as early as November 2000; however if you own one of these affected vehicles and are having trouble receiving California smog certification due to incomplete monitors or communications issues (Or are due for a smog inspection) and have not completed the recall, you should contact your BMW dealer.  It may help to refer to Emissions Recall 00E-A01 and BMW Bulletin SI B 12 15 99.