On these vehicles, if the exhaust warning light comes on and engine performance is poor, the following error codes may also be recorded.
P1550, synonymous with “boost pressure out of tolerance”.
P1556, synonymous with “boost pressure below lower tolerance limit”.
P1557, synonymous with “boost pressure above upper tolerance limit”.
As preliminary analysis, check the turbocharger’s blow-off valve and the subpressure line.
Another possibility is corrosion on the VTG turbocharger’s regulator linkage (variable turbine geometry). This may cause the linkage to jam sporadically, or even lock-up completely, so that the variable guide blades respond to the current load situation too late, or not at all. If a visual check indicates that the linkage is very corroded you should use mega macs to test the modulators. The linkage must be able to move freely and smoothly throughout its range, from one end position to the other, without jerking or stuttering.
You can restore the linkage’s freedom of movement by treating it with rust remover followed by spray-on grease. In intractable cases you will have to replace the entire turbocharger. If you have to do this, please follow the disassembly and reassembly instructions from the vehicle manufacturer.
Important safety note
Technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for use by suitably qualified personnel only.
Reprinting, distribution, reproduction, exploitation in any form or disclosure of the contents of this document, even in part, is prohibited without our express, written approval and indication of the source. The schematic illustrations, pictures and descriptions serve only for the purposes of explanation and representation of the instructions and cannot be used as a basis for installation or assembly work. All rights reserved.
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