DTC P0420 Catalyst System Efficiency Below Threshold (Bank 1)

So your check engine light is illuminated, and your code reader is spitting this out at ya:

DTC P0420 Catalyst System Efficiency Below Threshold (Bank1)

What, exactly, does this code mean? Is your catalytic converter at the end of it’s service life? The short answer here is Yes. Your converter is likely to be at fault for this code. Your vehicles On Board Diagnostics (OBDII) system monitors the upstream and downstream Oxygen Sensor readings and compares the switching of a rich-lean condition between the two.

The “upstream” O2 sensor, located in the exhaust stream before the converter, monitors the amount of oxygen in the exhaust gas as it leaves the engine while the “downstream” O2 sensor, usually located behind the cat or even in it, monitors the amount of oxygen in the exhaust gas after it passes through the converter.

When you first start your vehicle and the engine is cold, the upstream O2 sensor as well as the downstream O2 sensor will likely have about the same readings, as the gasses are not yet hot enough. Typically, the upstream O2 sensor changes from rich to lean very often as the engine computer adjusts the air/fuel mixture. However, when your vehicle reaches operating temperature, the exhaust gasses passing through the converter are hot enough to begin reacting with the metals inside of the converter ( platinum, rhodium and/or palladium – in some newer converters, GOLD! – Gold could actually increase oxidation, reducing pollutants even more!) and the downstream O2 sensor stays more so on the lean side.

Of course, that’s during normal operation. When the vehicle is at operating temperature and the downstream O2 sensor’s switching activity doesn’t tone down as per usual, that’s essentially telling the OBDII system that there is not enough oxygen coming out of the “cat”, so the converter isn’t properly oxidizing the hydrocarbons passing through it, the system sets a P0420 code and commands your malfunction indicator lamp on.

From here, you have few options if you want your Check engine light to go out – Replacement of your catalytic converter is looking more like the solution. In order to properly diagnose this issue, it is recommended that you bring your vehicle into a shop and mention to them your P0420 trouble code, allow that shop to do some trouble shooting and determine the cause and the fix.

However, for the DIY crowd, there are a couple of things you can check for before determining which action to take. Check for failure of the heated oxygen sensor(s) as well as an exhaust leak. If a faulty O2 Sensor is found, replace it. If you find an exhaust leak, repair it. Another possible cause of this code is a faulty PCM (Powertrain control Module). It can be difficult, if not complex, to test for these issues and a repair facility is recommended if you do not have the proper tools/instruments at hand.

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DTC C0265 – Brake & ABS Light Woes

I recently had the experience of dealing with this particular trouble code. The red brake light as well as the orange ABS light on the dash of a 2001 Chevrolet Suburban were illuminated. During the scan on the OBDII system, the code C0265 was displayed on my scanner and it was defined as this:

C0265: EBCM Relay Circuit (open circuit)

After doing a bit of research on this code, i’ve learned that this code is referring to a non-serviceable relay located within the EBCM (Electronic Brake Control Module) itself. However, there are several things that can (and should!) be done first, before anybody replaces anything! Let’s take a look at at the issue.

Circuit Description
The EBCM internal relay supplies battery voltage to all six valve solenoids and the pump motor. The low side of each solenoid coil has a feedback circuit to the EBCM microprocessor. When the relay is commanded off, feedback voltage is low. When the EBCM relay is commanded on, feedback voltage is high.

Conditions for Setting the DTC
C0265
The EBCM microprocessor detects low feedback voltage from all of the valve solenoids when the relay is commanded on.

When the DTC is set, this action is taken:

  • The ABS & BRAKE light indicators are commanded “on”.
  • The ABS is disabled for the remainder of the ignition cycle.
  • The EBCM aborts all other self-tests for components that are powered by the relay

DIY – Action you can take on, yourself

One of the first things I would do, is take the cover off of the Power Distribution Box under the hood. Check the owners manual or service manual for this vehicle & inspect any and all fuses that may have anything to do with the brake system. (While you’re under there, may as well check for any other bad fuses as well!

The next thing I would try, as per the research i’ve done, requires some tools and a little bit of patience. You may need a drill with a wire brush attachment as well as a ratchet & appropriately sized socket. I’ve read that some EBCM’s are unnecessarily being replaced due to a faulty ground, and at around $800.00 a pop, that’s too much money to “waste” unnecessarily.

Under the vehicle, in the frame rail directly below the drivers door is a ground cable. Possibly a few ground cables. If there are several, the one we’re looking for here is the thicker wire, probably a 12 guage wire. Remove it from the frame and clean the frame up nice with the drill & attachment. You’ll also want to clean up the ground strap where it attatches at the frame.

Once you’re done there, re-attach the ground to the frame & start your vehicle. If a faulty ground here is to blame, your troubles should be over and the lights will go out. If not, you may want to use your OBDII scanner (we all have one, don’t we?) to clear the trouble code. Test drive the vehicle to ensure the lights remain out.

If not, there is one other option you can try before you’re faced with a expensive bill. It’s been noted that a faulty battery to frame ground can also cause symptoms similiar to the above mentioned. Follow the negative battery cable from the battery to the ground on the frame. Perfrom the same cleaning steps above. If this doesn’t solve the problem, then the issue is highly likely due to the EBCM itself or the wiring leading to it. That’s a little more complex than the average DIY’er should undertake.

If the EBCM is deemed faulty and a replacement is necessary, just know it’s an expensive operation. The cost is probably around $800 or so for the part as well as an hour to an hour and a half’s labor time, plus programming charges, if necessary. This is exactly why you should perform the above steps first, hopefully you can save yourself a small fortune in these hard economic times!

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97 & UP Ford Trucks – ABS Light

As you may know, I’m an ASE Certified tech. At our shop, we work on many different makes and models of vehicles. I’m definitely not a Ford Specialist but I do work on a whole lot of them! I’m going to go ahead and say that’s just because there are so many of them on the road today!

That aside, we very recently had a 1999 Ford Ranger 4×4 Super Cab roll through our shop with an ABS light on. Almost immediately, I imagined it would be the speed sensor on the top of the rear axle as this is a common issue. After scanning her with the Genisys – we were given this code:

C1230: Speed Wheel Sensor Rear Center Input Circuit Failure

Turned out the initial suspicion of the rear speed sensor was correct. I replaced it with an aftermarket sensor from Advanced Parts which took all of 5 minutes and this took care of the problem. I cleared the code from the system and took her out for a spin. The ABS light has been out since.

I just wanted to share this bit of info as it’s a very common issue with these trucks, it isn’t very hard to repair at all and it’s pretty inexpensive. A job like this could be easily completed by a beginner DIY mechanic!

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