The check engine light came on, the code reader indicates PO122. What is the issue and what can I do. I am on a road trip.

what vehicle are you working on? Hard to trace circuits when the poster doesn't tell us the vehicle

use a code reader to reset the CPU program (possible program corruption from the battery change.)

if it happens again have the code pulled from the computer before clearing it out of the system.that is the only way you will know what the problem is and how serious it is.also have the charging system and battery checked.

Yes you did

PO 401 -- is an egr valve, you could have
bought when you got home, at the local auto
parts store for $90.00 & installed yourself

You never clear any codes or dash check lights
They are used to look up codes & diagnose
OBD2 System issues.

NOTHING goes away.

Those dash lights have been on all
vehicle for 30 years & indicate you have
a sytem malfunction somewhere.

could be a wiring issue to the tp sensor its self or a problem withe the throttle body or pcm

P0122 - Throttle Position (TP) Sensor Circuit Low Voltage, I would just replace the TPS as they are a known issue.

Many things could cause this issue. First of all; is there a check engine light? If not then it is probably a fuel-delivery issue, not many parts in the fuel system are linked to the computer and in turn do not trip trouble codes. If there is a check engine light then your local autoparts store should be able to scan and then you can tell us more.

See my the newer post from earlier today, similar issue. This is more likely to be a fuel mixture issue which triggers the check engine light as well.
Yes you should have it checked with a code reader anytime an indicator like this comes on and don't return to a mechanic who says to ignore it. Be safe , life is short.

You can disconnect your battery for 15 minutes or pull the fuse for an ECM or PCM fuse, but the best way is to visit any local repair shop. Most shops will have a universal Check Engine Light Code Reader that can quickly and safely reset check engine light trouble codes. It should take about 30 seconds.

Ask your local service center if they could reset the check engine light with a Check Engine Light Code Reader.

what your check engine light is doing is called the key dance.

The "Key Dance" is a coined term to identify a process of reading MIL fault codes stored by your cars engine computer (PCM). You cycle your ignition key from off to on (not start) 3 times leaving it on. You then count the number of times the Service Engine Soon light flashes. This combination of flashes identifies a fault code. For example, a code 21 would be flash, flash, pause, flash. All codes are 2 digits. Multiple codes are seperated by longer pauses. It should end with a code 55 indicating the process is finished.

Sometimes in newer models, the code is shown on the trip odometer. They would be P codes.

I would pull out my obd code reader and find out what it's telling me. Some parts places (Autozone, O'Reilys, etc) would even have a code reader you could borrow to check for any obd codes.