20/08/2026
Mercedes Citaro 2 RL SPV11 is back in service!
A case study of the work that can be involved in making a newly purchased vehicle reliable, and what our refresh programmes can comprise, along some photographs of what we’ve rectified along this journey.
Many issues due for attention first become apparent when run at operating temperature for a while, up a hill, when it rains and up to about 100 miles after the last time the fault codes were cleared by a computer. Once we know where we are with a vehicle, we decide whether to keep and repair the vehicle, or dispose of it.
This one has been the most substantial project yet, but we are committed to operating it. Our refresh programme has addressed the following matters:
- Saloon water and rust flake ingress. This was due to a corroded ventilator fan lip, cracks in the roof and expired window pillar seals.
- Driver’s cab water ingress - perished window seals and a hole drilled in the roof were allowing rainwater to infiltrate the cab.
These were seen to before she turned a wheel in service for us.
- Yellow engine management and emissions lights.
Following a genuine engine rebuild, she was self-reporting a crankshaft/camshaft timing issue. We fixed this and also put the tappets right as they were out of step.
She was also reporting a cylinder misfire. Examination of the injectors found that at least one was cracked. We removed all six injectors, put them into the bin, and replaced with new OEM injectors.
The injectors it had were putting the bus on a course to catastrophic failure. We found the engine oil was diluted and required replacing. Overfuelling led to excessive power delivery (not a good thing!) and excessive backpressure (definitely bad).
Unfortunately, the damage from the backpressure had already been done to the exhaust aftertreatment system. With the emissions light present, we removed the DPF and sent it off for cleaning as it was blocked solid with soot. This revealed that the adjoining Diesel Oxidation Catalyst had been severely damaged, with internal displacement immediately evident.
While the engine was being worked on, we took the opportunity to renew the components in the whole exhaust SCRT box. We also replaced the downstream Nitrogen Oxide sensor with a new OEM sensor.
- Intermittent low coolant warning despite the header tank being filled and there being no leaks. We replaced the coolant level sensor which resolved this fault.
- No saloon heating. We could hear the solenoid click when switching it on, just no heat. The boost pump which pushes hot water through the saloon pipes was dead, so we replaced it with a new one. All three saloon sidewall heaters were also dead. We replaced fuses in two of them to bring them to life. The third had a seized blower motor. We have lots of spare heaters from provincial Citaros that are no longer with us. We did initially save these for our ex-London Citaros, but these buses blow sufficient heat from the exchangers in the roof, so they were going spare. We cleaned all accumulated muck and dust from the heater matrices.
- Dashboard screen buttons unresponsive. We had to remove the instrument cluster and sent it off for repair. The button assembly was replaced which resolved the fault. This allows us to reset the trip mileage counter.
- We addressed several additional items for its first MOT with us back in March.
The work carried out should leave us with a warm, watertight and reliable vehicle. Since the injectors were replaced, we have noticed the performance has changed and the vehicle has slowed down a fair bit.
We’ve also noticed a change to the sound of the engine - it’s quieter in general. We will be monitoring performance very closely, observing frequency and length of DPF regenerations and whether the cooling fans will motor as often as they did previously.
Now the refresh programme is complete and we’ve been able to run it in service, we will be following the formal maintenance / service plan to keep it where it needs to be.
She’s been to Wales and back for a spot of rail replacement requiring PSVAIR compliance with and didn’t let us down - the motorway run was light work! We had hoped to do an engineering test run along our once proposed XV1 Cross Valley route, to evaluate the OM936’s capabilities (and fuel consumption!) in mountainous areas and compare with our OM906s, but didn’t get the chance this time. Definitely next time!
Some minor cosmetic changes will soon be applied and a livery is on the cards - watch this space!
