Mechanic Checks For Winter Operation

A Mechanic has to maintain vehicles accordingly depending on the conditions and adapt throughout the seasons which includes hot and cold weather. Since Winter is now upon us it's time to cover some preventive maintenance tips that experienced Mechanics are familiar with, but I want to share the basics with everybody.
Coolant Testing the coolant is of course very important and changing the coolant and thermostats should also be considered. Cummins promotes DCA (dry chemical additive) checks, to make sure the system is not overcharged or undercharged. DCA prevents liner pitting by reducing air bubbles forming in the cooling jackets. Changing the coolant (non lifetime brands) with the thermostats every 2-3 years isn't a bad idea since coolant eventually breaks down and the acidic build up that forms starts to eat up gaskets and castings.
Belts and Hoses who doesn't know the importance of these bad boys. They get the most abuse from constant tension, heat produced from driving the belts and hot/cold temperatures on the hoses. I always say "when in doubt change it out". Pulley bearings and belt tensioners need to be checked out and the cooling system should be pressure tested. School buses have 1 inch cooling lines throughout the bus interior and need to be observed for leaks and loose clamps.
Batteries batteries can either be load tested once a year preferably in the fall or changed when needed. Sometimes the latter happens at the most inconvenient time when it's cold, wind blowing ....a spare bus (in my case) needs to be fired up from a cold condition. So we generally do the yearly load test and go from there deciding what step to take next.
Block Heaters Most buses in our fleet have the conventional block heater system. Our plug-ins are timed in cycles to come on during certain ambient temperatures. We test them at every service to stay on top of  'no start' conditions in the cold. A couple dozen of our newer buses have diesel heaters that have timers so they come on a couple of hours before the run.
Tune Ups Mechanics know the advantage of keeping an engine tuned up. Easier starts less fuel burned is the main objective. Valve sets, fuel filters and air filters are all you can really do to a diesel engine especially with newer models. Checking for engine codes doesn't hurt, some codes do not light up on the dash and become inactive. Common sense helps in this area of maintenance and needs to be applied looking at everything that makes a highway vehicle function. The regular Mechanic or the 'Mechanic in you' can figure this stuff out.

Thomas Buses - Allison Transmission Wiring Modification

Thomas Buses are driven by an Allison MD 3000 Series Automatic transmission. This 1995 Saf-t-liner model had no power to the operators trans shift pad. The shift pad is also the Trans ECU [electronic control unit] so as I have said before always check the source , in this case the batteries.

There was a power feed open between the batteries and the rear control box at the engine compartment. I was able to limp the bus home by jumping battery power to the terminal board inside the control box which goes to directly to the operators cab supplying battery power to the shift pad/ECU.

This is obviously how I determined the open from the battery to the control box/terminal board [standard wiring on all Saf-t-liners]. The code for this fault is 35-00 [push both arrows on the shift pad at the same time with key on to retrieve code {under normal circumstances}

The control box at the engine compartment houses the engine intake heater components, lights etc. as well as the main battery power to the front electrical control box below the driver's side window.





My plan is to totally bypass the trans battery supply circuit from the battery to the ECU. Here you can see I've already cut the wires [larger #8 guage pos. and neg. wiring come from the battery while the smaller #10 guage pos. and neg. wires are running up front to the ECU]




This is the terminal board I mentioned earlier, factory wiring with spade connectors that connect the battery feed wiring to the trans. ECU wiring.

The first picture [top] shows the #8 pos. and neg. wires hooked up and running directly to the trans ECU. This will eliminate the extra #10 wires shown in the rear control box.


In the drivers cab the rear cover has been removed for easy access to the back of the trans. ECU. The upper plug can be removed and inspected for battery power. Both pos. and neg. #18 wires [2 each] run into this plug directly from the battery. The #8 wire is downsized under the dash to accommodate the smaller wiring into the ECU plug-in.



The 12V source from the battery is shown here with no connections in between. With a Digital Multimeter you can check for a battery voltage and a good ground.






So now you know when you have a shift pad with no reading [key on] the first thing to check is the battery voltage.

I hope this has helped you become more familiar with Thomas Buses equipped with Allison MD 3000 Series Automatic Transmissions.

Cummins Engine Repair- ISC Engine Code 434

Cummins Engine Repair not only involves mechanical but electronic repairs as well. The ISC model has an ECM that sends and receives messages that controls every performance aspect of this engine. The main source of power is the battery that depends on wiring that feeds the Cummins ECM sufficient voltage to run the engine systems.
Pictured is the laptop shot of an active code #434 a power interruption that derated the engine to a crawl. Derating protects the engine from sustaining high speeds and rpms which would cause more severe damage. This ISC Cummins Engine is in a 1999 Thomas School Bus Saf-T-Liner. With an active code you can retrieve it with the diagnostics switch [on the dash] & ignition switch turned on. The code will beep each number with a pause, in this case 4 beeps 3 beeps 4 beeps with a pause in between each #.

A closer look [click on photo to enlarge] shows numerous fuses on the positive feed wire to the Engine ECM [electronic control module]. Our code information is telling me there is a power problem so "the first thing to check is the Source."

Using a digital ohmmeter check the fuses for continuity and clean all the connections.

Note: Before this maintenance step I could not get a reading on my laptop, there was a communication error between the engine and the "Cummins Insite" software.
After cleaning all the connections and testing the batteries the communication problem was erased and the code disappeared.

There is a variety of 7.5 and 10 amp fuses inline with battery to ECU supply power. I traced the wiring back along the frame as well to check out any other possible problems. The rule of thumb in this situation is to check connections and wiring closest to the environment and work your way up the line.

Using a Snap-On Micro Vat Battery Tester I concluded that all the batteries were in good condition. This tester does a very quick assessment of battery condition and also tests starting and charging systems quickly.

The Conclusion to this problem was simple, servicing the battery connections which had enough resistance to cause the #434 code to occur. It makes sense since the ECM reads Voltage at a very sensitive level.

After an extensive road test the code did not come back and this experience was a good one telling me [and you the reader] to always check the simple things first!

Now we're ready for the next challenge with Cummins Engine Repair.

Recommended: Diesel Engine Repair Manuals

Thomas Buses HDX Electrical Panel

Thomas Buses have changed through the years and one model with a different electrical layout is the HDX. This 2004 has everything in a totally different layout compared to the Saf-T-Liner.





The Body Electrical [lights and accessories] Schematic is nicely displayed on the side door panel below the driver's side window.

[Click On Each Photo To Enlarge]





The circuit board shown here has been unfastened and tipped downward so you can see the many connectors that hook up with relays and battery supply junctions. There are 3 circuit boards in total with specific spots for each connector.








The circuit board is upright once again [located in the side panel] Here you can see the main battery power supply on the left with the many fuses and relays required to run lights, heater motors, solenoids etc.
The LED lights above indicate which relays are active, YELLOW
indicates the relay coil has been activated while the GREEN LED indicates the circuit is connected to the load.

Thomas Buses have evolved from the basic "battery to load with a switch in between" to complex relays & mult-functional switches that handle the demand for more circuits that can meet the load & safety component demands of today's School Buses.

DC Generators Fundamentals

Looking at DC Generators Fundamentals you can easily relate to Hybrid Automobiles which are powered by a fuel driven engine to create DC current that charges the batteries that drive the electric motors that drive the wheels.

Diesel locomotives are, for example, an example of a hybrid drive train, as the diesel engine does not cause the wheels to spin, but instead generates electricity that turns electric motors that then cause the wheels to spin.

There are two kinds of hybrid drive trains:

* Serial hybrid: The thing which turns the wheel is an electric motor, and the gasoline engine is used purely to generate electricity.

* Parallel hybrid: Both the electric motor and gasoline engine can cause the wheels to turn.

These "new" hybrid cars are all of the parallel design pattern. Not a one, so far, is of the serial design pattern even though that would be a much simpler vehicle to design and build. A simple-and-obvious-to-construct serial hybrid vehicle would be an otherwise pure electric car, and carry a portable generator.

When the batteries run low, fire up the portable generator and make some electricity. You could recharge the battery pack from the power grid, or from the generator, your choice. This could turn a limited range electric vehicle into one that could drive long distances.

However there are several steps of converting power (e.g. mechanical to electrical, and AC to DC). Each conversion step involves some lossage, and maybe this isn't the most efficient use of fuel.

The automakers are also working with a third type of hybrid, that they call "mild hybrid". [No information available yet]

It's not electric unless you can plug it in.

That is, many people seem to think the hybrid-electric vehicles on the market now are electric. Well, honestly, are they? None of them let you plug the car in to charge the batteries, none of them drive for any significant distance on pure electric, so how can one honestly think of them as an electric vehicle?

The electricity used in the electric motor, in all of these vehicles, comes from gasoline burned in the gas or diesel engine. These are not electric vehicles, despite the presence of that electric motor.

One day there will be 100% electric vehicles but technology will have to come up with a super/cost effective deep cell battery that will absorb and retain an amazing amount of amperage.

Here is a Youtube Video on a very old DC Generator that was steam engine driven back in 1917. It's a great example on how a driven DC Generator can be used to charge the battery pack [i.e. hybrid vehicle] or supply an amperage to a load. In this video the load is obviously the light being held for the demo...




DC Generators Fundamentals

Charging System Test - Heavy Duty 12 Volt System

A charging system test is a very basic operation with the right tools. Pictured is a Leece Neville 160 Amp Alternator which works very hard to keep the three 900 CCA [Cold Cranking Amps] bus batteries charged. Thomas School buses have a large demand with extra lights, electric motors and the engine air intake heater. The diesel engine in this case is a Cummins ISC Electronically controlled unit.



You're probably wondering what the heck is that device hooked up to the batteries? That's my tool of choice, a 'SUN' VAT 33 [Volt Amp Tester]. This model has been around for decades and still very reliable, our shop does have a digital tester but I like this one for doing a quick check on the charging system. The reason I'm testing the charging system is because of an unusually low voltmeter & ammeter reading.




The main leads are hooked up to the positive and negative battery terminals while the amps pickup is clamped around the positive cable to read alternator ouput back into the batteries. The engine must be running at high idle [approx. 1200 rpm]

The black control knob I'm turning puts a load on the batteries which should kick in the alternator to charge very close to maximum. Once I bring down the system voltage to 12V the alternator should normally put out a full charge of approx. 160 amps.

The test revealed the alternator is only putting out 80 amps maximum which will not keep up to the demands of a fully operational school bus & must be repaired or replaced.

This is a fast and easy way to do a charging system test on a 12 Volt Heavy Duty charging system.

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Testing Automotive & Heavy Duty Batteries

Here's a great video on testing a battery using the proper battery tester . There are many different battery testing models and they all work, all you want to accomplish is to put a load on the battery and read the voltage level. You need to know the CCA [cold cranking amp] rating labeled on top of the battery, then draw 50% of that off the battery with your tester for 10 - 15 seconds [the tester has a carbon pile that absorbs the heat from the heavy draw].

A general rule of thumb I use is a battery voltage drop of no less than 9.6 Volts after a 10 second load of 50% of the Cold Cranking Amp Rating. One important factor is the battery must be fully charged before testing, preferably around 12.6 Volts.

A battery tester is affordable but if you don't own one & you're not sure of the condition of your battery then a quick load test at a repair shop is worth it. A reputable shop won't charge you for the test if you buy a battery from them [since the test only takes less than a minute from start to finish].