Looking for help on a problem that has gone from intermittent to permanent. The latest limp home mode (LHM) came with engine running rough, sounding like a mild misfire/sputtering. Parts replaced include crankshaft sensor, both camshaft sensors, and throttle position sensor during previous bouts of LHM. The flashing ETC light is new, too. Multiple codes that are all over the charts: C121C, P161B, P2101, P2110, P2118, U0401, U1407, U1424, and U1425. Before this latest limp mode, the only code that ever popped up was P161B.
In all my years working on vehicles with computers, when multiple DTC’s show up that has nothing to with the others? It usually points to a bad computer.
The good news is, if the vehicle has less than 80,000 miles, the dealer has to replace the computer at no charge to you.
Vehicle has 95K.
I’ve got a bad coil pack, so I’ll at least try that first (replace the set) then explore the wonders of PCM replacement.
A few days ago my Corolla started very rough, ran rough and the CEL and traction light came on. Put it back in the garage and took the other car. A few hours later backed the Corolla out, running rough but not as bad, still had both lights on. Put my simple code reader on and it pointed to a bad coil on plug one. I swapped it with plug 2 to see if the problem went to 2 and the roughness went away. The connector may have been loose, corroded ???. But the traction light turned off and I cleared misfire code with my reader. Not sure why the traction light came on, my first thought was the computer going bad but everything is settled down and has stayed that way for several days.
Replacing coil packs and plugs didn’t change anything, though it was time for replacement. I focused on two of the engine codes then surfed for some troubleshooting videos. That led me to the throttle body. I removed it and heard loose parts inside. Convinced that the part was bad and I would obtain a replacement, I removed the cover of the sealed unit. Two of the three gears inside were stripped badly. I replaced the TB ($215) and the vehicle fired right up without warning lights. ETC relearn procedure completed and the Jeep ran fine … sort of. It now goes into limp mode after a few minutes of idle or when stopped at most traffic lights. No problems on the interstate. A repair shop did a complete scan and their own ETC relearn procedure ($79) and concluded that the TB is bad due to lack of one signal when vehicle is running. I will remove and replace the TB tomorrow. The repair tech recommended factory direct replacement from a dealer in the next town, but I’m opting first for a replacement part from the parts store since it was under warranty. The alternative is $292 from a dealer.
Good diagnosis job there OP. It sounds like you are on the right track. When replacing the crank/cam sensors and the throttle position sensor didn’t work, you were right to remove the throttle body for a bench top look-see. I expect once you get a properly working throttle body installed, you’ll be home free. There may be some re-learning the computer has to do though before it idles and runs perfectly again.
The problem has been isolated: it’s one of the connectors/plugs that attaches to the PCM.
It seems the problem was self-inflicted when I was troubleshooting the original problem, which was a very bad throttle body. But in the process, I did remove the PCM connectors. This vehicle has two large connectors to the PCM. Each connector has capacity for 96 pins, though maybe half of those are utilized on each connector. Thanks to the repair shop printing me the wiring diagram, I did some spark chasing and continuity checks. All were good. Before that, I had removed and inspected/cleaned the intake manifold and swapped out the air flow actuator. That was sheer pain. Anyway, I reinstalled everything yesterday and the jeep would barely run. I got MAP sensor codes. That was recently replaced, too. Re-seated the PCM connector and the engine was back to it’s other problem: fast idle after 2-3 minutes. Move the PCM connector ever so slightly and all kinds of other engine issues pop up. So now the challenge is the connector. Thankfully, it’s easy access.
Problem resolved – Throttle Body (replace only with OEM, original equipment)
Original TB was replaced with aftermarket. Subsequent TB change was also aftermarket. Bad decision. Although replacing the main wiring harness was necessary, it did not correct the new problem (idle surge after about 2 minutes and limp mode when stopped at traffic lights; DTC P2173). Two smoke checks confirmed no vacuum leak. Repair shop was correct – replace with OEM, original equipment. I finally did that. And I came close to replacing a perfectly good PCM.
I seem to be having similar issues. Only I haven’t replaced anything yet as mine just started this a couple days ago. I was just curious if replacing the throttle body should be my first step?
NO. Your first step is to get a proper diagnosis. What fixed the OP’s may not fix yours.