Pedestrian Celia Mary Service, 72, from Colwyn Bay, died when a car driven by a 90-year-old man hit a shop in Rhos on Sea, Conwy, in April 2012.
Her husband, David Service, 75, complained about how the north Wales force's investigation was conducted.
The Independent Police Complaints Commission (IPCC) has told North Wales Police to investigate his complaint.
The IPCC says North Wales Police is now obliged to carry out that investigation.
Mrs Service, a mother of two, died when a Jaguar car mounted a pavement and hit a shop.
Her daughter Helen, was also seriously injured.
An inquest later heard the vehicle had been travelling at about 27mph and Mrs Service died at the scene.
The driver, Geoffrey Read, was interviewed but he had no memory of the events.
Hospital tests showed he had an atrial flutter - or rapid heartbeats and poor cardiac function - which may have caused him to lose consciousness, although there was no record of him having had this before.
A verdict of accidental death was recorded and the inquest heard there would not be a prosecution.
Mr Service says that after his wife's death he became worried about how the investigation was conducted.
He had serious questions over some of the witness statements, and believes, among other things, there are discrepancies.
Following the IPCC's ruling, the force says it is duty-bound to examine or "scope" any new evidence or information to see if a case should be re-opened.
A pensioner is hoping North Wales Police will investigate the death of his wife.