Pulling Codes: The Story of U1016

Pulling Codes: The Story of U1016

This Pulling Codes article will center on issues involving the powertrain control module (PCM) talking to your scan tool. In many states, this is the controller our scan tool needs to talk to in order to determine if the correct number of monitors has run and passed. It's interesting to note that there appears to be two modes of failure in terms of communication.

U Code, Not Me Code

This has truly become the “theme song” of many modern-day controllers. This Pulling Codes article will center on issues involving the powertrain control module (PCM) talking to your scan tool. In many states, this is the controller our scan tool needs to talk to in order to determine if the correct number of monitors has run and passed.

It’s interesting to note that there appears to be two modes of failure in terms of communication.

The first mode is where the module will not communicate and has a U code stored in memory, it does not communicate on an enhanced or generic level.

The second mode of operation is where the module may not have a U code stored in memory, but communicates on an enhanced level, but not on a generic level. This mode has been the most challenging for many emissions testing states.

It is also interesting to note that the U code we have for our subject vehicle — a 2006 Pontiac G6 — has an ID number within the body of the code to identify which module is not communicating. The U code will always be stored in a module that does communicate with your scan tool. This is not an indication that there is a problem with the module that is talking; the module that is talking is pointing to the guilty party that will not talk.

A good example of this would be a BCM on a 2004 Chevy Tahoe, showing a code U1016 stored in memory; this indicates that it has lost communication with the PCM. The 016 within the body of the code identifies the PCM as the guilty party. A list of these ID codes appears in the service information for this year, make and model.

The question that now arises is “How do I test for a no communication issue?”

The first items you’ll need to verify are power and ground circuits for the data link connector (DLC). You first need to disable the vehicle so that it cranks, but doesn’t start. You’ll then perform a voltage drop check on the system ground. (The use of a DLC breakout box is preferred for testing, see Figure 1.) figure 1

Next, you’ll attach one meter lead to Pin #4 of the DLC and the other lead to battery negative with the ­engine cranking. You’ll perform the same test on Pin #5 of the DLC to battery negative as well. This is a good dynamic test that should show a voltage drop of 0.2 volts or less.

The next test on the DLC will be to check Pin #16 for battery voltage. You must always refer to service information to verify that you are testing the proper pins. See Figure 2. figure 2

The next step is to check communication circuits; there are terminating resistors that are used to reduce electrical noise on these communication circuits. A review of the schematics that refer to vehicle communication for the vehicle you’re working on is a valuable asset to properly diagnosing a communication issue. It’s strongly recommended that a DLC breakout box be used for testing.

The first test procedure here is to check between Pins #6 and #14 of the DLC with an ohmmeter. This resistance check should yield a resistance value of ­approximately 60 ohms (Figure 3). A system diagram is shown in Figure 4 as an example for review.figure 3figure 4

The next test is to check voltage information on DLC pins #6 and #14. Pin #6 is normally denoted as CAN H and Pin #14 is normally denoted as CAN L. The voltage information can be checked with a voltmeter or lab scope. If a voltmeter is used, it’s important to note that a peak min-max function should be used with a time testing window of 1 ms or less. The voltmeter cannot tell you the quality of the signal being produced. A lab scope gives a visual picture of the electrical quality of the signal that is present. (A sample pattern is shown for reference, see Figure 5).Figure 5

CAN H will have a voltage range of 2.5 to 3.5 volts, whereas CAN L will have a range of 2.5 to 1.5 volts. The wiring on the vehicle must be checked for shorts to ground, voltage or opens. If wires are next to each other, it’s also possible for wires to be shorted to each other. In many cases, frayed wiring has contributed to lack of communication on many of the vehicles tested.

It’s also important to be able to attempt communication with the vehicle on the generic as well as the enhanced side. It’s possible for it to communicate one way and not the other. When a vehicle is at the test facility, the communication attempt is made on the generic side.

In closing, the breakout box provides a way to view the communication activity under dynamic conditions. Always check all feeds, all grounds and serial data to a module before any replacement is considered.

In Review

Let’s now review our case study for this month. We have a 2006 Pontiac G6, in which the Tech 2 will communicate with the PCM, but a generic scan tool will not. The vehicle has been to the state test facility and doesn’t communicate with the equipment there either.

A schematic outlining the protocol architecture for the vehicle was obtained. It uses a GMLAN, which is CAN data. A schematic was reviewed first to see the architecture of the protocol. An ohm test was performed between pins #6 and #14 of the DLC, an ohm reading 0.505 Mohms was noted on the DVOM.

The terminating resistors for this vehicle are located in the PCM and BCM of this vehicle. The BCM was disconnected first and the same ohm test was run on the vehicle, this second ohm test showed 120 ohms. The BCM was reconnected and the PCM was now disconnected, this third ohm test showed 120 ohms. The PCM was reconnected and a final ohm test was performed on the vehicle. The final reading was 60 ohms.

It was now clear to this observer that a poor connection existed between the two modules. This Pulling Codes case is now closed. 

You May Also Like

Embracing Cutting-Edge Solutions the Industry has to Offer

Embracing cutting-edge solutions is strategic and imperative for technicians navigating the constantly changing landscape of automotive maintenance and repair.

Nadine Battah

Remember last month how I said 2024 was your year to be the technicians you always wanted to be? Remaining stagnant as a technician is simply not an option anymore if you want to be successful in the automotive industry. You must proactively seek out opportunities to embrace new tools, techniques and solutions that promise to enhance efficiency, accuracy and customer satisfaction.Embracing what’s new is strategic and imperative for technicians navigating the constantly changing landscape of automotive maintenance and repair.One of the top reasons I can give you for embracing new technology is the potential for improved diagnostic accuracy and efficiency. With the arrival of advanced diagnostic tools, like the Bosch ADS 625X, the Autel IA900, or the Hunter ADASLink, technicians can pinpoint issues with precision, reducing guesswork and minimizing the risk of a comeback. Whether it’s sophisticated tools or cutting-edge software solutions, the ability to leverage these new tools should empower you to deliver next-level service and drive positive repair experiences for your customers.Another thing to keep in mind is that embracing new technology and equipment opens doors to expanded service offerings. From state-of-the-art lifts and alignment systems, to specialized tools designed for specific makes and models, investing in the latest equipment enables you and other technicians to tackle a larger range of repairs and maintenance with confidence and precision. As the technology in cars continue to evolve, so too must the tools and equipment that technicians rely on to get the job done.Embracing new technology and equipment can also lead to improved productivity in the shop. By leveraging high-quality products that are specifically designed for today’s vehicles, you can streamline workflow, minimize downtime and deliver exceptional results for your customers.At TechShop, we understand the importance of embracing new technology, equipment and products in the automotive repair industry. That’s why we’re excited to announce the debut of our all-new “Tool Time” video podcast series, where guests from brands like Ingersoll Rand, Clore Automotive, SATA Spray Equipment and many more will sit down and join Eric Garbe and myself to discuss education and training on the latest products our industry has to offer.Join us as we embrace the future of automotive tool supply and equipment advancements together. And, be sure to subscribe to the TechShop newsletter to stay tuned!

Brake Lathe Basics

Resurfacing drums and rotors is a machining process with its own specific guidelines.

Refrigerant Oil Has to Be Right

Oil type is just as important as oil capacity.

Three bottles of refrigerant oil
Top 5 Tools: Steve Coffell, Auto World, Hazelwood, MO

Steve Coffell, a technician at Auto World in Hazelwood, MO, says his Top 5 Favorite Tools are: Related Articles – Lisle 61860 Oil Filter Housing Torque Adapter – Mueller Kueps Presents Redesigned Sensor Tap Series – Lisle Low Profile Fuel Line Disconnect   OTC Genisys Touch – Quick scan, bidirectional control Snap-on VANTAGE Pro –

Wheel Bearing Adjustment Tools & Equipment

A wheel bearing that’s out of adjustment can reduce bearing life and can affect more than just the bearing. It’s important to adjust the wheel bearing endplay to the proper specifications. If the bearing set is adjusted too loose or too tight, it can cause the bearing to fail prematurely. There are a few types of assemblies, so using correct procedures and tools will ensure a comeback-free wheel bearing installation.

Other Posts

TEXA Releases IDC5 CAR 76.5.0 Update

IDC5 CAR 76.5.0 is characterized by over 2600 new possible selections for the major makes on the market worldwide.

TPMS: Are Retrofits in Your Future?

Installing a retrofit kit can be performed with the tools and equipment you already own and use on a daily basis.

Tire tread
Maximize Your Scan Tool

Are you maximizing your scan tools to their full potential? Don’t let them be just an expensive code reader.

Scan Tool
2024 Is Your Year to Be the Technician You Always Wanted to Be

As we enter 2024, strategic career planning is essential for success in the automotive repair industry.

happy new year 2024