P0121 code
05-28-2017, 09:28 PM
#2
Technical Moderator
Join Date: 01-23-2009
Location: Fredericksburg, Virginia
Posts: 24,694
This link: https://www.obd-codes.com/p0121 is very different from what the HHR Service Manual says.
Mitchell OnDemand says that you should be looking for air getting into the manifold between the MAF and the MAP. Perhaps a malfunction of either the MAP or MAF.
Most likely the MAP is malfunctioning or a vacuum leak on the manifold
What they are saying is : it's not a problem with the throttle position sensor, it's a problem with what the sensor is sensing. I.E.: more airflow than expected.
On a 2006 I would inspect the rubber air horn, especially where the PCV hose attached, for cracks. Or the power brake booster vacuum line. Might even indicate a bad brake booster.
Another possibility is a bad connection at one of the connectors to the ECM.
Mitchell OnDemand says that you should be looking for air getting into the manifold between the MAF and the MAP. Perhaps a malfunction of either the MAP or MAF.
Most likely the MAP is malfunctioning or a vacuum leak on the manifold
What they are saying is : it's not a problem with the throttle position sensor, it's a problem with what the sensor is sensing. I.E.: more airflow than expected.
On a 2006 I would inspect the rubber air horn, especially where the PCV hose attached, for cracks. Or the power brake booster vacuum line. Might even indicate a bad brake booster.
Another possibility is a bad connection at one of the connectors to the ECM.
05-29-2017, 07:30 AM
#3
Member
Thread Starter
Join Date: 04-04-2015
Location: Old Monroe, MO
Posts: 37
This link: https://www.obd-codes.com/p0121 is very different from what the HHR Service Manual says.
Mitchell OnDemand says that you should be looking for air getting into the manifold between the MAF and the MAP. Perhaps a malfunction of either the MAP or MAF.
Most likely the MAP is malfunctioning or a vacuum leak on the manifold
What they are saying is : it's not a problem with the throttle position sensor, it's a problem with what the sensor is sensing. I.E.: more airflow than expected.
On a 2006 I would inspect the rubber air horn, especially where the PCV hose attached, for cracks. Or the power brake booster vacuum line. Might even indicate a bad brake booster.
Another possibility is a bad connection at one of the connectors to the ECM.
Mitchell OnDemand says that you should be looking for air getting into the manifold between the MAF and the MAP. Perhaps a malfunction of either the MAP or MAF.
Most likely the MAP is malfunctioning or a vacuum leak on the manifold
What they are saying is : it's not a problem with the throttle position sensor, it's a problem with what the sensor is sensing. I.E.: more airflow than expected.
On a 2006 I would inspect the rubber air horn, especially where the PCV hose attached, for cracks. Or the power brake booster vacuum line. Might even indicate a bad brake booster.
Another possibility is a bad connection at one of the connectors to the ECM.
05-29-2017, 08:39 AM
#4
Technical Moderator
Join Date: 01-23-2009
Location: Fredericksburg, Virginia
Posts: 24,694
"shop put on an aluminum intake"; The book says the manifold gaskets are prime suspects. Aluminum is more rigid than plastic, so I'm thinking you may need thicker O-rings on the TB and the head.
I would not trust that shop with DTCs. They completely mis read the description and didn't read the definition. The code descriptor is: Throttle Position Sensor PERFORMANCE. The condition for setting the code is: The ECM detects that the calculated airflow rate is more than expected.
There is not so much air that the ECM can't adjust for it, so you don't get P0171/P0172 lean condition. But it is more than the TP is indicating.
I would not trust that shop with DTCs. They completely mis read the description and didn't read the definition. The code descriptor is: Throttle Position Sensor PERFORMANCE. The condition for setting the code is: The ECM detects that the calculated airflow rate is more than expected.
There is not so much air that the ECM can't adjust for it, so you don't get P0171/P0172 lean condition. But it is more than the TP is indicating.
05-29-2017, 08:53 AM
#5
Member
Thread Starter
Join Date: 04-04-2015
Location: Old Monroe, MO
Posts: 37
"shop put on an aluminum intake"; The book says the manifold gaskets are prime suspects. Aluminum is more rigid than plastic, so I'm thinking you may need thicker O-rings on the TB and the head.
I would not trust that shop with DTCs. They completely mis read the description and didn't read the definition. The code descriptor is: Throttle Position Sensor PERFORMANCE. The condition for setting the code is: The ECM detects that the calculated airflow rate is more than expected.
There is not so much air that the ECM can't adjust for it, so you don't get P0171/P0172 lean condition. But it is more than the TP is indicating.
I would not trust that shop with DTCs. They completely mis read the description and didn't read the definition. The code descriptor is: Throttle Position Sensor PERFORMANCE. The condition for setting the code is: The ECM detects that the calculated airflow rate is more than expected.
There is not so much air that the ECM can't adjust for it, so you don't get P0171/P0172 lean condition. But it is more than the TP is indicating.
05-29-2017, 09:51 AM
#6
Technical Moderator
Join Date: 01-23-2009
Location: Fredericksburg, Virginia
Posts: 24,694
Idle relearn is just idling for 4 minutes.
What have you done to change the way the injectors work? What other engine mods?
The pedal controls the air, the ECM controls the fuel. Sound like the person tuning does not know enough.
My guess is you are getting bad MPG.
Have you looked at the EVAP purge valve? Disconnect it completely and blow through it; if it is free flowing it is bad and admitting unmetered air. It can cause P0171/P0172.
Since your car is not stock it is very difficult to diagnose on the interwebs.
What have you done to change the way the injectors work? What other engine mods?
The pedal controls the air, the ECM controls the fuel. Sound like the person tuning does not know enough.
My guess is you are getting bad MPG.
Have you looked at the EVAP purge valve? Disconnect it completely and blow through it; if it is free flowing it is bad and admitting unmetered air. It can cause P0171/P0172.
Since your car is not stock it is very difficult to diagnose on the interwebs.
05-29-2017, 10:19 AM
#7
Member
Thread Starter
Join Date: 04-04-2015
Location: Old Monroe, MO
Posts: 37
Idle relearn is just idling for 4 minutes.
What have you done to change the way the injectors work? What other engine mods?
The pedal controls the air, the ECM controls the fuel. Sound like the person tuning does not know enough.
My guess is you are getting bad MPG.
Have you looked at the EVAP purge valve? Disconnect it completely and blow through it; if it is free flowing it is bad and admitting unmetered air. It can cause P0171/P0172.
Since your car is not stock it is very difficult to diagnose on the interwebs.
What have you done to change the way the injectors work? What other engine mods?
The pedal controls the air, the ECM controls the fuel. Sound like the person tuning does not know enough.
My guess is you are getting bad MPG.
Have you looked at the EVAP purge valve? Disconnect it completely and blow through it; if it is free flowing it is bad and admitting unmetered air. It can cause P0171/P0172.
Since your car is not stock it is very difficult to diagnose on the interwebs.
05-29-2017, 10:38 AM
#9
Administrator
Join Date: 10-13-2011
Location: Welland,Ont Canada
Posts: 36,513
The system is off Bob from GDZHHR
https://www.chevyhhr.net/forums/feat...mission-51436/
These photos could explain some damages
https://www.chevyhhr.net/forums/feat...mission-51436/
These photos could explain some damages
05-29-2017, 10:57 AM
#10
Senior Member
Join Date: 09-16-2013
Location: Tampa, Florida
Posts: 1,408
Once you start putting aftermarket parts on you start getting aftermarket problems. You have done far too many modifications for your issues to be solved by conventional means. Every layer of mod is another potential failure point, unfortunately.
When it comes to cars you can have two of the following, never all three; CHEAP, RELIABLE, FAST
When it comes to cars you can have two of the following, never all three; CHEAP, RELIABLE, FAST