What do these codes mean 120d and 121B?

TABLETALK

MEMBER
2006 VOLVO XC70
2.5L
5 CYL
4WD
AUTOMATIC
162,000 MILES

Latest codes (and most often codes) 120D and 121B.

Engine acts as if it will stall at stop lights, sometimes stalls at start-up. Check engine light can be on or off when issue happens. A message says, 'Engine system service required'.
At low speed it can hesitate also, as if miss-fire.

New mass air flow sensor, coils and plugs, and new fuel filter. Smoke test showed 2 leaks, but those are fixed now, and still has the problem.

3 Replies

SQM

MECHANIC
6,383 POSTS

Hello,

There are a few reasons why you will get these codes.
It could be due to wiring issue with the mass air flow sensor, specifically having improper resistance. Which can be due to corrosion or oxidation of the connectors.
It can also be due to having blockage in the intake system, dirty throttle body, bad mass air flow sensor.
A good first step would be to inspect those components and clean as necessary. Also check for corrosion to the connector.

Take a look at these helpful cleaning guides:

https://www.2carpros.com/articles/mass-air-flow-service
https://www.2carpros.com/articles/throttle-actuator-service

I have attached some information about the codes below.

Let me know of any questions.
Thank you.

Images (Click to make bigger)