Tag axle (piston position) center lost due to hydraulic leakage
If no external leakage is found, the leakage is internal and the CVU will have to be overhauled, or replaced. Most common interal leakage is CBV1 and CBV2, change them first before changeing the entire CVU.
What you'll see
No driver-visible symptom recorded.
System reaction
Red Steer tag axle fault warn
Diagnostic depth
EST system could not keep steered axle at centered position during normal operation in fixed mode - the tag axle wheels are somewhat out of line.
• Internal leakage in CBV1 and/or CBV2 • Some form of leakage within the CVU. - external oil leakage at cylinder piston rod seal - external oil leakage at the fixation (threads or o-rings) of the OMV, DMV, or VPS - external oil leakage at the fixation (threads or o-rings) of the CBV1, CBV2, M1, M2 - external oil leakage at any of the CVU valve block plugs - external oil leakage at cylinder end caps - internal oil leakage at the cylinder piston seal