Marine Electronics Forum - Simrad AP26 Autopilot or power steering issue?

Autopilot will not hold a strong course on either auto or nav position. In the nav or auto position it will start drifting off course over a couple of miles and alarm will sound "off course" in the nav position. It use to work flawlessly until last few trips. Also wondering if the power steering might have air in system if this could cause problem?
Typically where is the AP reversible pump located in a sportfish and can it loose fluid or does it use hyd fluid?

try recalibrating the heading sensor ?

Are you having trouble holding a course manually? Usually the pump in in front of the P&S pump (hydraulically)

Have you moved anything around on the boat that might be messing with the APs compass?? A few steel coathangers in the wrong place can cause issues.

The AP pump is plumbed into the boats steering system so if you do have a leak somewhere the whole system is loosing fluid. How does the boat steer manually? From the symptoms you describe there are other things to check before looking for leaking fluid. That said it would be a good idea on a boat that sounds like it maybe new to you to verify that the system is not leaking.

You probably have air in a hydraulic line. I had the same thing happen and bleeding the system cleared it right up. End cap on the steering cylinder was just loose enough to cause a little loss of fluid and more injection of air.

I did install a vhf radio about the same time this issue started.

The easiest thing to do for a first try at solving is to recalibrate the autopilot.

In the installation displays of the system, found on the control head, are routines that compensate the compass for inaccuracies caused by nearby metal, and a routine that adjusts the A/P settings automatically to match your boat's handling characteristics. The compass part involves turning a circle while underway and the adjustment part involves letting the A/P take control of the boat and make some maneuvers, so it has to be done in a wide open area.

Look in your manual under the Installation section, or equivalent, for full details.

This is the first thing that has to be done in making sure the A/P can steer the boat accurately.

And since the problem showed up right after the VHF install, recalibration may fix it.