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Put car in reverse while driving....Check Engine Code reads PO 171

While driving in a storm over the winter, I hit a skid and reverted to my old days of driving on ice (in a different stick-shift car). I tried to down-shift our '98 Camry (automatic)…so I placed it in reverse. It stalled. The car continues to run, but the check engine light has been on since that day.

I took it into a nearby garage the next week and they couldn’t find any engine issues that time. They turned off the check engine light. It came back on the next day. I went to Advanced Auto Parts and got the code read: PO 171.

Since then, I’ve been driving the car once or twice a week, saving up $$ before taking it to my new repair shop – to which we’ve switched for our other car. What might I expect to hear from them about our Camry? Am I damaging the car by continuing to drive it?

Many thanks.

PO171 is "Fuel Trim System Lean (Bank 1) ".

Probably not, but I’d feel better making that statement after first diagnosing a few things. The good news is that the code was triggered by the oxygen sensor and not by the knock sensor. The bad news is that we don’t know what the codes were before the CEL was cleared.

That code indicates that the engine is running “too lean”, in other words, too much air/not enough fuel. The cause could be as simple as a disconnected or cracked vacuum hose. Frequently, you can hear the “sucking sound” from the problematic vacuum hose, but sometimes you can’t. Anyway–this is a cheap and easy fix if that is the actual cause.

If there is no vacuum hose-related issue, then two other things to check are the O2 sensors in the exhaust flow and the Mass Airflow sensor (MAF) on the engine air intake. A disconnected wire leading to an O2 sensor can cause this problem, as can a bad O2 sensor. On a '98-vintage car, it is very possible that you are due for new O2 sensors. The MAF can likely be cleaned if that is the source of the problem.