HP Officejet 7310 carriage jam

I'll start by explaining some of the components you need to understand to troubleshoot the carriage system.

The Carriage is the thing the cartridges are mounted in, it slides on the carriage rail, the bushings in most newer carriages are made of plastic, (or maybe it would actually be called a polymer, or composite material). The bushings are the pieces that wrap around the carriage rail.

The carriage rail is a shiny round rod that the carriage rides on, it is driven across the rod by the carriage belt, by the carriage motor, at the opposite end of the belt there is an idler pulley, ".

In a HP printer the device where the carriage parks, (sits at), when the machine is not printing is called the service station, it is responsible for cleaning the print heads, and for capping the heads when you are not printing, (so they won't dry up). The bottom of the service station is the "Spittoon Base", ink is spayed into the base before printing to prime the heads, there is an absorbent pad in the base to soak up the ink. Note that the pad does not always soak up all the ink, so if you tilt an HP printer you can spill the ink out of the service station, (especially if it is a heavily used printer). The piece that moves back and forth in the service station is the "Sled", it was wipers to clean the heads on it, and the caps that keep the heads from drying out are also part of this assembly. The sled is moved back and forth before the carriage leaves the service statio to wipe the heads, this happens after the heads are primed, then the carriage is moved off the service station and the sled is again moved back and forth to clean the wipers.

The encoder strip is a plastic timing fence that looks clear at first glance, but has black lines painted on it. The strip is threaded through an optical sensor on the back of the carriage.

When the printer initializes the carriage has to leave the service station, or, if the machine was powered off when the carriage was somewhere else, whatever spot it is sitting in, and travel the way to the other side of the printer, and then return to it's home position which is the service station.

When the carriage reaches the side of the printer away from the service station it sets that as a reference, then it counts lines on the encoder strip as it travels home, if it doesn't see enough lines before it gets all the way to the other side and can't move any more then the printer decides the carriage must have something blocking it.

Sometimes a service station will fail in a way where the sled does not retract fully, if that failure happens when the carriage is parked then the carriage will usually not be able to leave the service station. If the service station binds when the carriage is off of the station, then the station may not be able to move all the way to that side, and will detect a carriage jam. When the service station binds you might hear a grinding noise as it's motor tries to drive the sled back and forth.

If the encoder strip is dirty the printer may not see all the lines and detect an error, often when the strip is dirty the carriage will move too fast and slam to one side of the printer.

I use water to clean the encoder strips in HP printers, water works well on water based inks, if your printer uses ink with another base you might use alcohol, but "ONLY" if the ink is not water based.

One end of the encoder strip is attached to a spring mount, if you wipe the strip starting at the end that is attached to the frame, and wipe only towards the spring mount, then the strip will stay attached to the printer.

A dry carriage rail will cause the carriage to bind, if the carriage does not move fast enough a carriage jam will be detected. Some newer HP printers use grease on the carriage rail, many models use a liquid lubricant, Use "ONLY" light synthetic or silicone based lubricants on printers that use a liquid lubricant, Petroleoum based products may melt the plastic bushings and ruin the carriage. (YES, Petroleoum based means WD-40)

some HP printers have a timing disc on the service station, and if the service station binds, or the timing sensor fails they report a carriage jam, but as far as I've seen that jam always occurs before the carriage moves.
You can use a synthetic lubricant on the carriage rail :hope this helps