Series 60 Coolant Level Fault

This week on the Series 60 we had a Coolant Level Low fault to fix. This code was set last week when we tried to get it running after refilling it with the coolant we drained. The system uses a coolant level sensor in the fill tank on top of the radiator.

Active fault code for Coolant Level set by the ECM, as shown on the scan tool.

Our first task after retrieving the code off the ECM was to refer to Detroit Diesel's Power Service Literature to find out what exactly this code means and what procedures are recommended for troubleshooting.

Looking up service literature for this fault code.

Detroit Diesel recommends ensuring that coolant level is actually correct first.

Coolant fill tank on top of radiator, with coolant level sensor right above the radiator fan.

What we found after taking the pressure cap off was the coolant was indeed low. It took almost 2 gallons to fill it up to the correct level where we could see it in the tank with a flashlight.

No more coolant fault code.

The service literature says that following this procedure, the fault code should no longer be set. Of course, we cleared the rest of the codes manually, but there was no active fault for coolant level after we put the scan tool back on the truck.

My reflection:

It's not always a bad sensor or faulty wiring that can set a fault or cause a problem. Sometimes it's the simplest solution that is the correct one. So here our first question for a "coolant level low" fault on a truck should be, "does it actually have enough coolant in it?" And our first action should be to check that it does.

Sometimes it's best not to overthink things and keep it simple.

Sensors & Scan Tools

This week we finished testing the list of 5 sensor we were given to remove and test. Among the list:

1. Thermistor.
2. Pulse generator.
3. Variable-capacitance pressure sensor.
4. Piezo-resistive pressure sensor.
5. Potentiometer. 

The first 4 we tested off a Series 60, and the last one, for ease of access, we tested off a running stand-engine, a Cummins ISX 600.

Test procedures vary for these sensors as they operate on different principles, but the similarities all these sensors share is that they are designed to send a voltage signal back to the ECM to let it determine engine operating conditions. This information can then be used to adjust output parameters such as fuel injection timing, or used as fault detection for driver warning systems.

We also broke out the scan tool and used it to help test these sensors. A multimeter works just as well, but a scan tool can be faster and easier. For instance, we hooked up a gauge and pressure booster to the manifold boost pressure sensor, and with it connected to the ECM and the scan tool hooked up to the truck, we were able to match boost pressure in PSI on the pressure gauge and on the scan tool. This tells us the sensor is good and working as intended.

This could also be done with a multimeter, but would specifications telling us how to interpret voltage readings to a corresponding pressure value.

Applying pressure to the manifold boost pressure sensor with our pressure gauge.

Scan tool data from the ECM match our pressure gauge readings, indicating that the sensor is working as intended.

My reflection:

Not all these tests went flawlessly. We had some technical difficulties involving a crankshaft position sensor, which would not produce voltage when a magnet or piece of metal was passed across it, and a throttle position sensor which gave us readings in reverse of what we expected from specifications. We will likely be revisiting these next class.

The question I might raise then is how would a technician in the field deal with these technical difficulties? How would their methods differ from ours? Did we perhaps make a mistake in our tests, or is there an actual technical problem with the sensors, electrical systems, or tools we were using to test them?

Crankshaft Position Sensor

This week we moved on to "pulse generator" sensors. These include wheel speed sensors for ABS, crankshaft position sensors, and camshaft position sensors.

For ease of removal on the Series 60, we chose the crankshaft position sensor. It is simply bolted to the bottom of the block and works by creating a magnetic field as the crankshaft gear turns, sending voltage signals back to the ECM. A missing tooth is used to tell the ECM engine position.

Crankshaft position sensor prior to removal.

Crankshaft position sensor after removal.

My reflection:

We did not get to test this sensor yet, however it can be tested by putting a multimeter across the electrical terminals and reading voltage as a magnet is passed over it. Failure of this sensor could result in a cranking, no-start condition.

Worth noting on this sensor was how difficult it was to remove due to the fact that the O-ring had swelled up. It took a fair bit of prying and pulling to get this thing out of the engine. Just another testament to the fact that when working with vehicles... it's hardly ever as simple and straight-forward as the textbook says!

Is it -40F or 250F? The ECM can't tell!

This week we took our coolant temperature sensor and heated it in boiling water with our ohmmeter on the electrical part of the sensor. As the sensor's temperature increased, the resistance values went down. From around 3k (3000) ohms resistance at ambient temperature, it fell to just 300 ohms at close to 212F. The sensor is working as intended.

Next we backprobed the electrical connector which runs from the ECM to the sensor and hooked up a variable resistor. At this point, the truck has no coolant in it, the engine is stone cold and not running. We turn the key on and hook up a scan tool to the truck, going to the data stream where we can look at what the coolant temperature sensor is doing.

With resistance set low, the temperature gauge on the dash of the truck is redlined at 250F, matching what the scan tool data stream reads. The truck's ECM thinks the truck is overheating, though in reality the engine is cold. As resistance is increased, the temperature goes down on the dash gauge and on the scan tool data stream. We can make the truck think it's -40F when in reality it's the middle of summer.

Variable resistor backprobing the ECT sensor's connector.

Variable resistor. With this we can lie to the ECM and make it believe the engine is overheating when in reality it's not even running.

The engine is not running, but the ECM believes it's overheating.

Scan tool data showing what the ECM sees. Hmm interesting to note EGR temperature is -40F?

My reflection:

A modern vehicle uses a wide variety of inputs from sensors all around the vehicle, including engine sensors, transmission sensors, wheel speed sensors for ABS and traction control, the list goes on. It uses these inputs to determine the current operating conditions and tweak as necessary for optimum performance. If any of these sensors is faulty or otherwise giving incorrect information back to the ECM, the ECM will act accordingly.

For instance, if the ECT is faulty and giving incorrect information, similarly to how we lied to it with our variable resistor, the truck may be going down the road and think it is overheating when in reality it is just fine. Most modern trucks today would respond to this by derating the engine and forcing the driver to pull over and shut down to prevent damage. All because a sensor or its wiring was faulty.

The primary lesson to be learned here? Modern technicians will have to understand how these sensors work, as well as the electronic and electrical systems they are incorporated into. Without that knowledge, we cannot properly diagnose a fault with these systems.

Engine Coolant Temperature Sensor

This week we pulled the engine coolant temperature sensor off the Series 60. It is located on the right side (passenger) toward the rear of the head and block. It is an NTC-type thermistor which measures engine coolant temperature by changing resistance (temperature goes up, resistance goes down) and sends a voltage signal back to the ECM, which uses the information, along with that from other sensors, to adjust to a wide variety of engine operating conditions.

The sensor can be tested by comparing ambient temperature to resistance. One could also heat up a small container of water, stick the sensor in and measure resistance as long as the temperature of the water is known.

Coolant temp sensor and specifications for temperature and resistance.

Coolant temp sensor.

My reflection:

Removal and testing of this sensor shouldn't be any big deal on a typical engine, what might present a problem is finding specifications for it. It took longer to find specifications (appreciation to our instructor for finding the correct ones) than it did to pull the sensor and make measurements.

The moral here? Sometimes the hardest part of the job isn't turning a wrench, it's finding information! Without information, we would have little idea what correct resistance values are at what temperatures, and be unable to reliably diagnose this sensor.

Organization & Cleanliness

They say that "cleanliness is next to godliness." This week our Electronic Diesel Engine Controls class was cancelled to due illness, so I will use this week's blog post to focus on a general issue which may be a problem for some automotive and diesel shops.

If you were to walk into our shop right now, you might find things like this:

I don't think this is where we put the grease gun after use.

This is just sloppy and unprofessional.

My reflection:


Without an organized shop, tools will be harder to find, may end up lost, stolen, or even present a tripping or other hazard if left on the floor. Leaving tools where it is most convenient instead of where they belong after use is lazy and unprofessional.

Cleaning up messes is part of the job. Oil, coolant, and other fluid spills are not only an inconvenient mess, they are a safety hazard. Clean them up ASAP! This means more than throwing floor dry on it and driving off.

Finally, does leaving trash laying around everywhere really need an explanation?

It reflects poorly on the professionalism of a shop and the character of its technicians when they cannot be organized, clean up messes, or even clean up their own trash. It would be the first and last time I would ever let a shop work on my vehicle where the technicians used it as a coffee table.

Thermostat Housing On The Series 60

This week my team was assigned to work on the FLD Freightliner which has a Series 60 engine in it. Our first task was the testing of various sensors, starting with the engine coolant temperature sensor. This meant draining the coolant and pulling the thermostat housing off the engine.

The coolant is drained either at the driver's side radiator drain valve on the bottom side of the radiator, or a drain plug on the bottom radiator pipe. We drained it at the latter, and my suggestion if draining it here is to wear safety glasses and be ready to get out from under the truck quickly as it will pour out fairly violently. Coolant doesn't taste very good, for the record.

Next we began pulling hoses off the thermostat housing. There is one hose which goes to the upper radiator, another which goes in the side of the thermostat housing from the water pump, and another small hose with a 14mm fitting that runs out from the top to a fitting on top of the radiator.

A lot of hoses and pipes!

Drain pans, not a very good picture. That tire step makes climbing up on the truck easy!

Thermostat housing with the upper radiator hose removed. Note heat shrink clamps, this is the first time I encountered one.

My reflection:

I have worked on this engine before but one thing that struck me was the replacement of the old, often-seen worm and spring clamps with a new heat shrink type. I had never encountered this type of clamp before. To remove them you have to heat them up with a heat gun and cut them off with a knife.

These clamps, although not reuseable, are supposed have a better clamping force than traditional clamps. Will we perhaps see more and more of these on newer trucks and use them as replacements whenever we work on the hoses of older trucks using traditional clamps? Time will tell, but I definitely learned something new this week!