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Billy, Trainer/ Master Technician
Category: Hyundai
Satisfied Customers: 3548
Experience:  Trainer 8+ years, master tech. 10+ years, SAE member
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Hyundai i800 2.5 crdi D4CB engine. Can run smoothly no

Customer Question

Hyundai i800 2.5 crdi D4CB engine. Can run smoothly no problem starting but ocassion ally goes into limp mode. Turn key off then on it clears. No lights on dash. Fuel filter and turbo and EGR valve and rail pressure sensor have been changed, also injectors but still does iy
JA: Have you checked the fuses? The dashboard bulbs?
Customer: Yes all good
JA: What year is your Turbo?
Customer: 2010
JA: Are you fixing your Turbo yourself? What have you tried so far?
Customer: New turbo, new EGR valve, recon injectors, new fuel filter, new rail pressure sensor, new lambda sensor
JA: Is there anything else the Mechanic should know before I connect you? Rest assured that they'll be able to help you.
Customer: No just that it's driving me nuts. I don't see anything else that I can change
Submitted: 12 days ago.
Category: Hyundai
Expert:  Billy replied 12 days ago.

Hello and Welcome! I'm Billy and i will assist you with your inquiry. Feel free to ask if any further info is needed.
If you get prompted for a Premium service or a phone call, please ignore that, as i don't think it is needed at this point.

My apologies for the delay, thank you for your patience.

Expert:  Billy replied 12 days ago.

When an engine goes into limp mode, it means that codes are stored within the engine control unit.

Did you check for fault codes? and if yes, what fault codes are you getting.

As these codes should provide us with direction. We will know which parts, systems or wiring we need to check. And we will proceed accordingly

Customer: replied 12 days ago.
A check light has only come up on the dashboard once, when checked fault code P1186 low fuel rail pressure but usually no fault codes are thrown up when it hapoens
Expert:  Billy replied 12 days ago.

If no codes are thrown, then it should not be limp mode.

Maybe it's just the dpf trying to regen.

When the problem happens, do you try taking the vehicle on a highway, and go on for arouund 20 minutes with the rpm higher than 2000, as this should complete the DPF regen procedure.

Customer: replied 12 days ago.
It has no DPF. This is the pre DPF model
Expert:  Billy replied 12 days ago.

That actually is a good thing, one less system to worry about.

Expert:  Billy replied 12 days ago.

So, again, if there are no fault codes, then this would not be limp mode.

Can you please explain in detail what happens when the vehicle doesn't behave normally?

And did you check other modules for faults? (other than the engine module)?

Customer: replied 12 days ago.
The car starts as normal. It drives as normal sometimes for around 10 miles, sometimes 2 miles, then when you press the accelerator to accelerate the power suddenly goes and the car will not do more than 2000 revs. It appears to happen when the revs reach 2500 rpm. Keep it under 2000 rpm seems OK. When it happens it keeps running fine no miss fire etc but takes a long time to increase speed. Turn key off and back on it resets and drives normally. No lights come up on dash
Expert:  Billy replied 12 days ago.

Could you check it with a scantool when it does the problem, before turning the key off?

As there should be a fault code, or many. They maybe listed as pending fault codes.

Customer: replied 12 days ago.
The only one that our diagnostic scanner has picked up is P1186
Expert:  Billy replied 12 days ago.

Well, that code will cause a limp mode. It will cause the symptoms you described.

Since you have already replaced the sensor, i would suggest checking the wiring to that sensor.

Expert:  Billy replied 12 days ago.

You can check with ignition on:

terminal one on the pressure sensor to ground, you should get 4.5 to 5.5 volts

On terminal 2 (signal wire) to ground you should get around 0.5 V with ignition on. around 1 to 1.5 v at idle, and around 2.5 to 4.5 volts at full load.

That will confirm, the sensor is working correctly, so check the wiring for any problems.

One way to do that, is to have you live data on the scan tool, and wiggle the wiring harness, and look for changes in pressure reading.

Customer: replied 9 days ago.
Thanks, ***** ***** checks come out OK.
Expert:  Billy replied 9 days ago.


As the problem is intermittent, did you check when the problem was current?

Customer: replied 9 days ago.
if the revs are kept at or under 2000rpm the car drives fines. If I accelerated harder the car goes into limp but no lights on dash
Expert:  Billy replied 9 days ago.

In this case, i would check the circuit between the tank and the high pressure pump. Since we have no apparent problems on the high side, the low side would still cause problems under high demand.