In Depth Diagnostic and Scan: Buying Instrument Time

• the electrical department that performs the repair
• having the finding priced as a scope

• a full systems survey instead of a single fault

• Super C chassis and coach network boundaries
• apparatus body control diagnostics
• tractor fault tracing between shifts

Every network the unit carries, read and saved

Chassis modules and coach side multiplex are both scanned, with codes and freeze frame data exported before anything is cleared.

Voltage drop measured under real load

Circuits are tested with current flowing rather than with a meter on an open circuit, because a bad connection reads perfectly at rest.

Current logging where the fault is intermittent

A recording logger stays on the suspect branch for hours or overnight. This is the reason a session sometimes needs a second day.

Gas and combustion measurement where appliances are involved

LP pressure read on a manometer while the appliance fires, with a second appliance loaded to expose a supply that sags under demand.

Thermal survey of load centres and connections

A thermal camera over a distribution panel and battery terminations finds resistance that a meter reading at rest will never show.

A written finding with the numbers in it

You receive the readings rather than a verdict. If the finding leads to a repair here, the diagnostic hours credit in full against that invoice.

1. 1

   Capture the story before touching the unit

   20 minutes

   When it happens, what else was running, how long since it last happened, what has already been replaced and by whom. On an intermittent fault that history often decides where the logger goes, and it is information no instrument can recover.

2. 2

   Read and save everything before clearing anything

   45 minutes

   Chassis and coach networks are scanned and the codes and freeze frame data exported first. Clearing a fault before recording it destroys the only trace of an event that might not repeat for a fortnight.

3. 3

   Test the circuit under load

   1 to 3 hours

   Suspect circuits are loaded and voltage drop is measured across each segment, with grounds checked separately at the chassis stud. This step distinguishes a high resistance joint from a failed device, and those two present identically.

4. 4

   Log the intermittent rather than waiting for it

   4 to 16 hours

   Where the fault will not perform on demand, a recording logger goes on the branch and the coach sits. Overnight parasitic draw work and heat related faults both need this, which is why a session occupies a bay rather than a slot.

5. 5

   Write the finding with its measurements

   45 minutes

   The output is a numbered finding: which circuit, which reading, what it should have been, and what the repair is. Where the answer is that nothing is wrong with the component the owner expected, we say that with the figures attached.

• A fault that appears and clears with no pattern anybody can describe
• Several unrelated warnings arriving on the panel at the same moment
• House batteries flat after four days parked with everything switched off
• Lights or a slide that work when cold and stop once the coach warms up
• A code somebody read at a parts counter and then cleared without recording it
• One appliance that misbehaves only while a second one is running
• A generator that starts and drops out under load but idles cleanly for an hour
• Two shops have already replaced parts and the original complaint is unchanged

• A high resistance connection rather than a failed component, which reads as a dead device and measures as a voltage drop under load
• Parasitic draw from a module that never goes to sleep, found only by logging current across a full night rather than by a spot reading
• Ground path corrosion at a chassis stud, which produces symptoms across several unrelated systems and presents as multiple failures
• LP supply pressure that measures correctly at rest and sags once two appliances draw on it together
• A multiplex switch input rather than the device it controls, so replacing the device changes nothing at all
• Codes cleared before anybody saved the freeze frame data, which destroys the only evidence of an intermittent event

• Multi protocol chassis scan tooling for J1939 and J1708 on Freightliner, Spartan and Ford F53 platforms
• Cummins and Allison drivetrain diagnostics on diesel coaches, read alongside the coach side network
• Lippert OneControl, Firefly Integrations G series and Spyder Controls multiplex diagnostics
• Precision Circuits and Intellitec load centre and battery disconnect testing
• Victron, Xantrex and Magnum inverter charger communications and configuration verification
• Fluke meters with clamp accessories, a recording data logger, a thermal camera and an LP manometer

• Clearing a fault code before somebody has recorded it and its freeze frame data. On an intermittent fault that record is the entire evidence base.
• Replacing a component because a code named the circuit it sits in. The connection into that circuit fails far more often than the device on the end of it.
• Charging a flat bank and calling the problem solved. A bank that dies in storage has something drawing on it, and charging removes the symptom for four days.
• Adding a second inverter, a bigger bank or more solar to cure a voltage complaint. Undersized capacity and a high resistance connection produce the same symptom, and only one of them is cured by spending money.

The sentence I say most often in this bay is that the code is a postcode, not an address. It tells me which street the problem is on. People arrive having bought the part the code appeared to name, sometimes twice, and the actual fault is a green ring inside a connector or a ground stud that lost its star washer in 2015. So I load the circuit and I watch the volts, because a bad joint measures perfectly at rest and only shows itself with current going through it. When somebody has already paid two other shops, I start by asking what was replaced, then I go and test the thing everybody assumed was fine.

What does the one hour minimum on diagnostic time actually cover?

Getting the unit into a bay, connecting tooling to the chassis and coach networks, exporting codes and freeze frame data, and reading the history. That setup is most of the cost. A repeatable fault is often solved inside the same hour, and the hour credits in full against an authorized repair.

Why does a stored fault code not tell you which part has failed?

Because it only reports that a controller saw a value outside its expected range on a circuit. The component, both connectors, the ground and the harness are all candidates. Connections fail more often than devices. We load the circuit and measure voltage drop, since a bad joint reads perfectly on an open circuit meter.

How do you catch a fault that only shows up once a week?

With a recording logger on the suspect branch and the unit left armed in a bay. Heat related faults get the coach parked in sun with thermocouples fitted. That is why some sessions run into a second day, and it is the only method that reliably catches something which will not perform on request.

Do you scan coach side multiplex systems as well as the chassis?

Yes, and it matters. Lippert OneControl, Firefly Integrations, Spyder Controls and Precision Circuits panels run lighting, slides, tank levels and climate through modules and a network. A chassis only scan reads half the coach. On a multiplex system a dead fixture is frequently a module output or a switch input instead.

What is a parasitic draw test and why does it need a whole night?

It measures what the unit keeps drawing after everything is switched off, using a clamp and a logger on the negative. Modules take anywhere from twenty minutes to four hours to actually sleep, so a spot reading taken in the afternoon proves nothing. Logging through the night shows which branch never settles.

What happens if the session finds nothing wrong with the part I suspected?

That is a common and useful outcome. You get the measurements showing the component is within specification, plus the finding that does explain the symptom, which is usually a connection, a ground, a supply pressure or a configuration. The billed hours still credit against any repair you authorize here afterwards.