Sensor Faults TD5

As I’m having trouble with my TD5 Defender “kangarooing” under hard acceleration, I did a bit of googling and asked questions on the usual forums. The kangarooing is apparently a known issue caused by either:

  • injector seals being worn
  • injector harness has oil in it
  • MAF sensor issues
  • Fuel regulator fault
  • Fuel pump fault

Well the pump was whining like a randy mosquito, so that got swapped, the injector harness swapped and the injector seals replaced. The red plug (C0158) at the ECU was removed, cleaned and replaced. No oil visible in there but worth a look. The turbo wastegate actuator was rusty, so I had that replaced when the car went in for MOT, thinking the garage can test the boost better than I can.

Still has the problem.

MAF disconnected next. Went for a drive and saw no difference. MAF was getting power. Maybe it was duff. New MAF, no difference.

I invested in a (budget) diagnostics tool from iCarsoft i930 to read what was going on. The Engine warning light isn’t coming on, so it isn’t anything the ECU is too concerned about, but I want it fixed.

The Error codes were:

  • Manifold pressure circuit fault logged low
  • Inlet air temp circuit fault. logged low
  • Multiplex input circuit fault logged low
  • 1% reference voltage fault logged low
  • Driver demand 3 fault logged low

Manifold pressure reads as 42.75kPa and Ambient pressure as 0kPa. Science tells us air pressure at sea level is 101.325kPa, so something is weird!

As my TD5 is an early one, the lack of Driver Demand 3 isn’t necessarily a problem. Searching online, suggestions are roughly:

  • One of the sensors is duff and throwing out everything else
  • The ECU has in it oil due to the injector harness
  • The ECU hardness is worn and shorting out

The two sensors dealing with air pressure and temp share a common earth pin at the ECU and the pressure readings obviously require some kind of investigation.

I bit the bullet and replaced both sensors. The MAP/IAT was particularly gunky, so when a previous owner blanked the EGR, they didn’t bother cleaning the manifold or sensor, so I am pleased I swapped it out.

Gunky, due to the EGR which was blanked off long ago, but why blank the EGR and not swap the sensor? Well, because they cost about £100

The pins powering both sensors are live at the ECU and the sensor plugs, errors won’t clear on the iCarsoft and the problem persists.

Visual inspection of the harness indicates it looks sound, but maybe time to rip it out and replace it?

PSI Powerbox

The fact there is a PSI Power box wired into the ECU harness probably isn’t helping. It gives a kick of extra fuel when pulling away, but I have it unplugged for now whilst I diagnose what is going on. The box is a fudge to avoid doing a remap for more power, in combination with a bigger intercooler. My ECU is a “10P” variant, the chip is soldered on and not writable unless it is removed and a socketed one soldered in its place. Using this box avoids that.

As the intercooler in the car is stock, the poor old turbo is going to be working a bit harder than designed and to remove it from the troubleshooting, it is getting unplugged. Maybe once this is resolved and I invest in a new intercooler, I can plug it back in or rip it out entirely and get the proper remap done. But that is all for another day as there is no point remapping a duff engine….

From internet searches, it does seem other people have similar fault codes with the iCarsoft i930 on a pre-2007 Defender, despite the fact the device supports older ones like mine and has a menu option for it on the screen.

So, after mulling this over, I hired a Nanocom.


The Nanocom shows a few alerts, all of which are benign as I don’t have any of these things fitted:

  • 10,1 aircon
  • 10,3 tachometer drive
  • 10,4 gearbox/abs
  • 10,5 aircon clutch
  • 14,1 aircon fan
  • 14,3 tach drive
  • 14,4 gearbox/abs
  • 14,5 aircon

Nothing about the AAP, MAF, multiplexer etc.

There are also two other logged faults. One refers to the EGR being stuck closed (20,5), which is expected as the engine has an EGR blank fitted. The other…..

So a test drive showed the problem:

1.36 bar is a little bit high….

The TD5 engine will boost around 1.2bar with a stock intercooler. 1.4 is where the overboost kicks in. so When my the Nanocom is reading 1.36, it soon trips to 1.4 and the fuelling is cut by the ECU. On the Nanocom, the boost drops immediately to about 0.3, the engine “kangaroos” and the overboost condition is logged. So how do we fix this?

First let’s check the sensors are actually working, because we know the i930 warned they were duff:

They look fine and change as we drive. So sensors are good!

So how to fix the overboost?

There are some gizmos that can fool the ECU to ignore overboost, but the overboost control is there to protect the engine and I’d rather wind it back and make the bouncing go away. The correct way to handle this is to wind out the wastegate rod, making it longer and thus vent the boost pressure earlier. “Longer is lower”.

First I marked where the rod was set to:

Then used a 10mm to undo the lock nut and adjusted the rod so more space showed between the mark and the lock nut.

So what happens now? well, the boost only reaches 1.28 and no “kangarooing”. The Nanocom no longer logs an Overboost. Hooray!

With trial and error, I could wind it back a quarter turn, drive and test it and repeat until I know where the sweet spot is, but I don’t have the time and only hired the Nanocom for a week. I’ll look to buy one in future, but for now, I’m happy enough.