What's B anyway?

Before you go diving into diagnostics, you probably feel you have a grasp of what everything in your plans and schematics mean. You understand your tools, and have a general plan of attack. But every so often, you’ll find letters and numbers in places you don’t expect them. That’s what happened this month in our first case study.

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Botched 2006 Honda CRV
By Alex Portillo, TST member

Here’s how it all began. A local veterinarian wanted to add his own tow hitch, because if you work on animals, you can certainly work on your own car, right?

After cutting up a bunch of wires in the rear of the Honda, he took apart the fusebox and put it back together. The result was a burning smell, a no start and inoperative windows. Realizing he was over his head, he took it to a local body shop. They replaced the body control module and fuse box, and then gave up. In addition to the original problems, now the horn would sound anytime a scan tool was connected to the Diagnostic Link Connector (DLC). That’s how it ended up at the Car Clinic, our shop.

I was always the B-tech, assigned to tires, brakes, front end and simple diagnostics. I was never given the tough cars, but now it was finally my turn. First, I knew that the customer cut some wires open in the rear of the truck for the trailer lighting. I found that he disconnected the brake light failure sensor and cut the wires so he could plug in his trailer harness. After testing with my Powerprobe that the wires were not shorting the multiplexer in the passenger fuse box, I decided to get the wiring schematics for the horn circuit and the computer data lines.

Pin No. 5 of the DLC is the signal ground for the communication network and when it was grounded the horn was going off. I confirmed this with my Powerprobe, so I started with that wire and was curious to see where it led. The wire for pin No. 5 is brown with a yellow tracer and it is connected to the Immobilizer, fuse box, and Powertrain Control Module (PCM). I immediately suspected a damaged PCM (though not totally bad, I still had communication) and/or an Immobilizer issue. I opened up the PCM and I noticed that it had internal burn spots.

I studied the DLC schematic and I noticed that the ground was entering the passenger side fuse/relay box and it had “B18” notated on the diagram. I had seen a similar notation earlier somewhere. The horn circuit happened to have a light green with blue tracer wire with the “B14.” What’s “B” anyway?

I looked on Mitchell 1, and “B” apparently stands for “connector B.”

The horn relay gets power from fuse 47 in the underhood fuse box, but the control side for the horn relay is the light green/blue wire from the passenger fuse/relay center. This passenger multiplexer has 16 fuses and 11 connectors. The light green/blue wire was the control side for the horn in the same connector B that held the ground lead from the DLC. I may be on to something.

Taking a closer look at the multiplexer, I noticed it also had the letter “B” in the connector slot. In fact, there were more letters (A through K) and numbers (1 through 11) apparently used to identify the separate slots. But the connectors all fit into the same slots. Take a look how similar they all look and how many connectors there are! I theorized that maybe the wrong connector was plugged in to slot B.

I printed out all the connector views and I inspected the multiplexer to see if the right connector was there. I was able to identify connector B by locating the color wires I was dealing with.

Connectors B and G were flipped. The body shop simply plugged the harness into the wrong spot. I put the connectors where they were supposed to be and the car started immediately. Oh yeah, and no more horn blaring in my ear with my scan tool connected. I have to admit, I felt pretty good about the outcome of my first major diagnostic assignment.

5 Minute “No Start” Diagnosis By G. Truglia, president of ATTS and TST)

You can diagnose almost any no start in five minutes. How? Here is the five-minute plan of attack:

Engine Mechanical: Do a cranking vacuum test to see if the valves are opening and closing. For those with a scope, this test is simple and quick. All you have to do is connect the leads to the battery (positive to positive / negative to negative) and couple the scope to AC volts. Follow this by disabling the fuel and cranking the engine over. Now you are ready to perform a relative compression test. You can also perform this test with an amp clamp that goes around either negative or positive cable while the scope is set to DC volts or it’s amp set up.
Fuel: Add propane to a manifold vacuum source, vacuum line, or brake booster intake hose to see if this gets the engine started. If you have a gas analyzer, stick it in the tailpipe. If you read over 2,000 PPM HC (Hydrocarbons), fuel is not your issue.
Spark: Check for spark with a spark tester. If there is no spark, perform an RPM check by using the rpm Parameter Identifier (PID) on your scan tool. If you have rpm, that means you have primary ignition on most vehicles and there isn’t an issue with the crank sensor.

Don’t forget to join in for the first Motor Age/TST webinar of the year, “Performing a Professional Brake Job”, on Feb. 21 at 8 p.m. Eastern. Sponsored by Wagner, this webinar will be full of tips on proper repair and avoiding comebacks. You can register for this free webinar at www.motorage.com/brakejob.

And lock down March 23^r on your calendar for the 10^th annual TST Big Event. Held at the Ramada Inn and Conference Center in Fishkill, N.Y., this all day event will feature two great instructors: John Thornton (teaching GDI with a focus on VW/Audi) and Dave Decourcey (presenting misfire strategies for today’s cars). In addition to great instruction, attendees will also be eligible for door prizes throughout the day.

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