Richard Shane also lowered his price target on Ally to $33 from $35, which implies a 5.1% increase from the stock's closing price Monday of $31.41.
In premarket trading Tuesday, the stock declined 1.34% to $30.99.
The stock has risen 38.61% year to date.
According to Bloomberg, the average Wall Street price target for Ally is $38.35. The stock had 17 buys, 3 holds, zero sell ratings previously, according to Bloomberg.
Ally is scheduled to report earnings on Oct. 16. Analysts surveyed by FactSet expect the bank to post a profit of 98 cents a share and net interest income of $1.19 billion.
The company last week said its online brokerage and wealth management arm would cut commissions to zero per trade from $4.95 starting Oct. 9, joining a wave of online brokers that dropped their commissions following a move by Charles Schwab (SCHW) - Get Free Report .