The attack occurred at about 9.45am (0545 GMT) in Karada, a commercial area of the capital, said police Major Abbas Mohammed.
Three of the wounded were soldiers, police said.
Soldiers at the checkpoint were waving at the driver, trying to get him to stop, when the explosion occurred, smashing windows in nearby buildings and damaging cement walls surrounding some, Mohammed said. Six parked cars were damaged, including one that caught fire
Iraqi police and the army sealed off the area.
Elsewhere in the capital, a roadside bomb killed a US Army soldier whose convoy was patrolling south-eastern Baghdad on Friday night, US military sources said.
Armed men also killed a member of the commission charged with ensuring former members of Saddam Hussein's Baathist regime are banned from the Iraqi government, police said.
Thirteen commission members have been killed since it was created two years ago.
Overnight, police and hospital officials reported heavy fighting in the Euphrates River city of Ramadi.
The US military reported the deaths of two more soldiers in and around the city, the scene of nearly one-quarter of 29 American deaths this month.
At least 1913 US service members have died since the beginning of the Iraq war in March 2003.
The US military declined to say if it was conducting a large offensive against Ramadi, but police and residents have reported heavy fighting there during the past week.
"There are 30 to 40 battalion-level operations going on across Iraq on any given day," said Lieutenant-Colonel Steven Boylan, a US military spokesman in Baghdad.
"What you are seeing is the pattern of operations that we have been conducting almost every day here."