Mechanic 12 Volt System Troubleshooting-Reverse Warning System Stuck On

Working on a fleet of buses has some amusing moments. Especially when 12 Volt systems and moisture come into play. Mechanics go to school to get the basics, then you need to use those basics and go much deeper. Experience indeed is the best teacher and mechanic information on symptoms and troubleshooting can be shared and recorded for the benefit of the entire shop and right here on this blog for future use.

Below is what I call a 'Mechanic's Special'

The driver complaint is the back up alarm and reverse lights come on all the time even in neutral. So the first thing to think about is what could possibly cause this to happen without touching the controls. With the key on we have full operation of the back up warning system. The HDX Thomas pusher we are working on has the VIM (vehicle interface module) mounted above the steering axle (Lots of snow and ice). This is the first place to check since the interface module receives the reverse signal from the Trans ECU after the driver selects reverse.   CLICK ON PICTURE TO ENLARGE.

The VIM has relays and fuses (BELOW) to control the circuits on the chassis side of the bus including the high idle, neutral start and reverse warning. Luckily once we pulled off the lid to the VIM we heard a buzzing noise. This is not normal and is a mechanic troubleshooting red flag, you want to look for abnormal mechanical situations.

After opening the VIM up the problem was obvious. The corrosion was making a circuit from battery to the reverse warning system. Moisture, oxygen and 12 Volt electrical circuits love each other and create double trouble after uniting for a given period of time.

Here is my 'KEEP IT SIMPLE' drawing (BELOW) of the circuit in question. The operator chooses reverse, the transmission shifts and the reverse signal is fed to the Vehicle Interface Module to the reverse relay and 12 Volt power feeds the reverse alarm and lights.

Once you know how a circuit works it makes the problem solving much easier and common sense will prevail. This problem can happen anywhere so be prepared. Checking electrical problem circuits and components closest to the environment pays off more times than not. I hope you got something out of this Mechanic Information.

Please leave a comment below and share any 12 volt electrical experiences you've had in the past or just let me know you got something out of this info.

International DT Engines Overview

DT Engine Design & The Wet Sleeve

International DT Engines have a wet sleeve meaning the cylinder wall is a seperate machined part that presses into the engine block. The sleeve is in contact with engine coolant which is why it comes by it's description "Wet Sleeve"

International runs the wet sleeve design because it increases the durability and the cylinder wall thickness has a much better heat transfer which allows the cylinders to stay round when going through thermal expansion. Also, the cylinder sleeve is much harder than the cast block cylinder making the DT design much more wear resistant.

Rebuilding the DT Diesel Engine is very convenient since the block stays in the frame, hence the term "In-Frame". The sleeves being removeable saves the block from damage since the sleeves are replaced during the inframe process, saving time and extra costs.

With standard cast engine blocks the cylinder bores have to be machined. If there is major damage, in some cases the block might not be salvaged. Standard block cylinders become out of round during thermal expansion and wear much faster than the stronger DT steel cylinder sleeves.

DT Engine Fuel Injection 

DT engines used a Bosch pump-line-nozzle (PLN) mechanical direct fuel injection system  from 1984 until late 1995.  DTs used a Bosch MW style pump 1984 through 1992, while the  Bosch P style pump came into force between 1993-1995 where the New Generation Diesel engine design began, which is still the same basic block design.

Up to 1997 mechanical injection was used but in rare occasions. Emissions tightening started in 1994 and the injection systems were redesigned using electronically-controlled unit direct fuel injection.

HEUI (Hydraulically-actuated Electronically-controlled Unit Injection) injectors, co-developed by Navistar and Caterpillar were unleashed from 1994 to 2004. From 2004 the engines use Electro-Hydraulic Generation 2 Unit Injectors nicknamed "G2 injectors".


Recommended

Troubleshooting Electronic Diesel Engines

Troubleshooting electronic diesel engines can be a headache if you don't have the troubleshooting software required to check for codes. This is the first step when there is a amber or red code indicator light on the dash.

Once you rertrieve the code you can get a general idea what part of the electronic system to start focusing on. It may be a lost signal from a sensor or an innacurate signal that the computer (ECM) picked up.

Computers being as logical as they are will pick up on anything that is not within parameters according to the way they were programmed. This is a grreat advantage to your troubleshooting process.

Don't rule out the basics. A poor connection causing resistance will fool the ECM on the amount of resistance or voltage a sensor relays back to home. Always check connections both positive and ground starting at the battery.

There have been several instances in my shop where a poor ground has been the root of many electrical problems especially with electronic systems. So the first step is to check the electrical source thoroughly and then hook up the laptop.

If you send me a question about an electronic diesel engine with a code on the dash, I will tell you to follow the sequence in the above paragraph. It's reality now, every shop running or servicing electronic diesel engines need to have the proper software to get by with day to day operations.

How To Troubleshoot Air Brake System ABS Code .

This ABS system is by Meritor Wabco found on most highway transport vehicles. An ABS light on the dash indicates a problem that has to be repaired since an ABS fault is a fail according to Motor Vehicle Inspection criteria. The ABS system does not operate normally when there is an active code.

The code description reads "Right Front Wheel Sensor - Open"

When looking at the Right Front wheel the sensor looks like it's intact. The first thing to check is to make sure the sensor is pushed all the way into the housing. The sensor reads a tone wheel on the hub and sends a signal to the ABS Control Module.

According to the troubleshooting specs the resistance of the sensor should be between 900 and 2000 ohms. When I checked it out there was no continuity causing an obvious open circuit as indicated by the fault description. The first step is to check the wiring itself for any damage or the possibility of a faulty sensor. Most times exposed wiring to the environment is at fault when troubleshooting a circuit problem.

Further inspection shows a spot on the sensor wiring that has rubbed through on the brake pot assembly. One of 2 wires has been damaged and caused the open circuit condition. I use heat shrink butt splices since they seal very nicely from the environment.

Once the sensor was replaced I moved the bus in a forward direction & the ABS warning light went out. This was an easy fix and it was nice to stumble across the bad wire in an easy to reach location. This conventional school bus is a only a year old but you never know what can happen to wiring and components when operating on a daily basis. I hope this mechanic information has helped you out and maybe you will have it as easy as I did with repairing this failure.

The Best Diesel Engine-DT 466 International School bus

The Best Diesel Engine? By far the DT 466 by International. For the Medium Duty fleet operator this engine is the most reliable of all. Pictured is the DT 466 E [electronic version]. Each injector is controlled electronically by the engine ECM and injection is actuated by high pressure oil. These injectors are HEUI [hydraulic electronic unit injector] that are reliable but typically have to be resealed if there's a fuel in the oil problem...for example.














Here I'm setting valves which is .025 for both the exhaust and intake. One of the differences with the electronic engine and the older non-electronic models is the newer engines have the intake manifold built into the valve cover so it weighs much more, making it difficult to remove. There is the Engine Control Module as well fastened to the valve cover on the driver side.

Below is an electronic unit injector that can be tested while running with a laptop for proper injection cycles.















On the International School Bus the dog house inside the cab also has to be removed to gain access to the rear cylinders. This aside the reliability of the DT 466 E and older DT 466 in my opinion is the most reliable model for a medium duty fleet operation. One characteristic with the electronic version is a very rough start up in cold weather because of the engine oil pressure feeding the high pressure system. It takes a bit of high idling to get smooth fuel injection happening.

If you can find a mechanical DT466 then you have reached diesel heaven! With no HEUI and a Bosch fuel injection system you will have very dependable power unit. I can remember in-framing these engines for $1200.00 they are very basic and easy to work on. But technology has taken over and fuel emissions are here to stay.