If you were injured during the course of your employment, you are still entitled to pursue a workers' compensation claim, despite a failed drug screen and despite the fact that your employment may be terminated as a result of the failed drug screen. Workers' compensation is a no-fault system, so the cause of the accident is irrelevant, although if you were injured by the negligence of a third party (not you or not your employer), you may be able to pursue a personal injury lawsuit against the negligent party, in addition to a workers' compensation claim.
If you were injured in the accident, you should claim workers' compensation benefits. However, If the cause of the accident was because of intoxication, that would be a possible defense to any workers' compensation claim. The w.c. carrier would have to prove that you were the cause of the accident and that the accident was because of intoxication. If the accident was caused by another driver or If you took the drugs after the accident because of pain caused by the accident, that would be different from intoxication causing the accident and would not bar your claim.
Again, if you were the cause of the accident, the passenger may have a personal injury claim for his injuries. The claim would probably be against both you and your employer. Because you were in the course and scope of your employment, your employer should cover any such claim. They, however, may assert that you were outside of the course and scope of your employment because either you weren't supposed to take the customer home or, again, intoxication.
Recommendation: If you were injured in the accident, make your w.c. claim and see what the employer/w.c. carrier do with it. If it is denied, consult an attorney.
If you are served with a lawsuit as a result of the passengers injuries in the accident, turn it over to your employer and ask that they defend you. Also turn it over to your own car insurance company just in case the employer does not defend you.
There are plenty of excellent w.c. attorneys in Sacramento. Find a good one here at www.avvo.com or at www.caaa.org. CAAA is the association for attorneys here in California who represent injured workers. Or you can call me for a referral.