If your steering does not work, one possible cause could be a damaged steering servo or receiver.
If your throttle servo is still responding correctly then it is unlikely your servo, it is important that you test the steering servo to narrow down the problem. Simply unplug the servo that is not working from the receiver and plug it into the other servo channel.
For instance, if the throttle is working but steering does not seem to respond, unplug the connector that is installed into channel 1 on the receiver and plug it into the channel 2. Of course you'll need to temporarily unplug the throttle/brake servo in order to perform the test. Operate the throttle trigger to test the steering servo. If the servo still does not work, then it's time to replace it. If the servo operates normally when installed on a different channel, then it's the receiver that is causing the servo failure.