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Can You Drive A Diesel Vehicle Safely in Mexico? by Ted White


Mr. White is a well-respected authority on diesel engines and this open letter is published with his permission. Depending on the results of the presidential election in 2018, this may all be moot. Already (summer 2018) foreign firms are selling fuel in Mexico. A limited amount of foreign (USA.OPEC) fuel is already being imported. In 2019, they were expected to start importing mainly foreign refined fuel. Meanwhile there is a 50/50 chance the diesel fuel you buy in Mexico will be ULSD.

FOR 2007.5 - 2015 PICKUP OWNERS

For those new to this topic, Mexican diesel fuel presently contains up to 500 ppm of sulfur, while the Ultra Low Sulfur Diesel (ULSD) sold in Canada and the USA is just 15 ppm.  Unfortunately, the higher sulfur Mexican diesel can cause temporary “sulfur poisoning” of the emissions system for some pickup trucks with diesel particulate filters (DPF) and selective catalytic reducers (SCR).  (DPFs were introduced in late 2007, SCRs were added by Ford and GM in 2011, and Dodge introduced SCRs in 2014).  Your pickup truck has both DPF and SCR technology if you add Diesel Exhaust Fluid (DEF) to a separate on-board tank.


Despite the potential for emissions system problems on DPF/SCR equipped pickups, laboratory testing prior to 2007 suggested that 2007.5 through 2010 model year diesels, whether Ford, GM, or Dodge, would tolerate well the higher sulfur Mexican diesel.  This has indeed turned out to be the “real world” situation.  There can be occasional bluish exhaust smoke during regeneration cycles, but no serious fault conditions are triggered. In addition, testing prior to the release of DPF equipped pickups confirmed that there would be no permanent damage to the emissions system, as long as higher sulfur fuels were not used for more than 40,000 continuous miles.

For 2011 and 2012 model years, some owners have been experiencing occasional engine light illumination, and “DEF QUALITY POOR” warnings. Those warnings typically disappear, however, following a 15 minute high speed run, OR during subsequent heavy trailer towing, OR after the next regeneration. All of these situations usually raise exhaust gas temperatures high enough to purge sulfur compounds from the system.

DEF QUALITY POOR warnings tend to occur a few weeks after a fifth wheel or other heavy trailer has been disconnected, and the truck is being driven around locally in Mexico.  Lower exhaust temperatures while unloaded permit the buildup of sulfur compounds, reducing the efficiency of the emissions system until an error code is triggered.  The Diesel Exhaust Fluid is NOT the culprit in these cases, even though that is the message displayed.  It is simply a matter of the engine computer thinking that higher than expected NOX (oxides of nitrogen) in the exhaust is evidence that the DEF is not doing its job.


In 2013, Environmental Protection Agency monitoring requirements for NOX in the exhaust became much stricter. Monitoring is more frequent, and NOX must remain within a tighter tolerance level. In addition, regenerations to burn off the soot and sulfur compounds are less frequent.  As a result, 2013 and later model year diesel pickups are more likely to register fault codes while in Mexico, and clearing the codes is more complex.

Also for GM 2013 and later model years, the distance which can be travelled after a DEF fault is triggered, and before “limp mode” (maximum speed 4mph) is initiated, gets accelerated with time.  This means that the available non-limp-mode miles often disappear more quickly than warranted by the distance travelled, creating a stressful experience for owners.

Luckily, not every owner will experience such fault conditions, but when they happen, the key is to get the truck to do a regeneration as soon as possible.  Once the emissions system is cleared of sulfur compounds by the heat of a regeneration cycle, the engine computer stops thinking that there is a problem with the DEF, and the fault condition disappears.  It is critical that a regeneration be initiated well before limp mode occurs, because the vehicle must be driven at highway speeds for about 35 minutes during a regeneration.


Unfortunately, there is no direct method for an owner to force a regeneration, but some pickup models have an indirect method based on EPA requirements that regenerations must occur approximately twice as often if there is a problem with the DPF pressure sensors.  So, disconnecting the DPF pressure sensors can sometimes force a regeneration, provided that more than half the normal distance between regenerations has already been travelled.

Typically, immediately after disconnecting the DPF pressure sensors, the driver will see a message that soot filter cleaning has started and to keep driving at highway speeds until it is finished. If half the normal distance between regenerations has not yet been travelled, it could be up to 200 hundred miles before a regeneration is triggered, but odds are, for a fault to have been triggered by excess sulfur buildup, it is likely that more than half the normal distance since the last regeneration has already been travelled. Information is available from the author on how to unplug the DPF pressure sensors on some 2013 and later model years, but forcing a regeneration is significantly more complicated if limp mode has already occurred.

Unfortunately, in mid-February of 2015, Pemex cancelled the ULSD refinery upgrades it had announced in September of 2014 - upgrades which would have made ULSD available across Mexico by early 2016.  This means that most Mexican diesel fuel will continue to be LSD for the next few years.  For those traveling the Baja though, there is reasonable evidence that Pemex stations in the Northern Baja are all carrying ULSD originating in the USA or Japan.

Irrespective of the manufacturer of your pickup, if it also requires Diesel Exhaust Fluid, be sure to take at least 7 gallons with you into Mexico, because DEF consumption will increase, and even double, as the system tries to compensate for temporary sulfur poisoning of the emissions system.  DEF is available from some Napa Auto Parts and heavy truck service centers on special order, but the price can be twice as much as in the USA.

Owners needing more specific information, or with a personal experience to share, can contact me at Please note though that the information provided in this article, and to any owners who need assistance, is provided only in the interests of sharing of knowledge, and should not be interpreted as an endorsement or encouragement by the author for owners of 2007.5 and later pickup trucks to drive them into Mexico. 

Ted White
April 26, 2015


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