No MAF signal voltage from E40 ECM
Thread Starter
Teching In
Joined: Aug 2021
Posts: 7
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No MAF signal voltage from E40 ECM First post from a rookie. I apologize in advance for the many mistakes I'm likely to make.
I have a fresh rebuilt LH6 (Gen IV 5.3) in a 2005 Saab 9-7x. Engine details below. It runs and moves fine, but I had an MIL and it was a code for failed MAF. Purchased a new MAF and still no go. Tested voltages at the connector using the testing steps in post 10. I have good 12v, good ground (0 Ohm) but have only a few mV on the signal wire. From what I'm reading, this should be around 5v. I traced the wire and validated against the E40 pinout that it is C3 pin 11. Checking voltage directly at the wire on the back of the connector still returns only a few mV. I have validated that all fuses are healthy and I've run out of troubleshooting ideas. I'm afraid I have a bad ECM...
I've read through dozens of threads on this site and others, but don't know where to go from here. Looking for some suggestions or confirmation that I indeed have a bad ECM. Please ask if you need info that I have failed to provide. Thanks in advance!
Build details if interested (or applicable) :
2005 LH6 Alum 5.3 w/E40 ECM
.020 over bore w/new HE pistons/rings/rotating assembly balanced
BTR Truck Cam v2 Stage 2
Speed Engineering headers
Single high-flow cat
Bank 2 O2 deleted
4l60e Monster rebuild
HP Tuners MPVI2 Pro
AEM Wideband
I have a fresh rebuilt LH6 (Gen IV 5.3) in a 2005 Saab 9-7x. Engine details below. It runs and moves fine, but I had an MIL and it was a code for failed MAF. Purchased a new MAF and still no go. Tested voltages at the connector using the testing steps in post 10. I have good 12v, good ground (0 Ohm) but have only a few mV on the signal wire. From what I'm reading, this should be around 5v. I traced the wire and validated against the E40 pinout that it is C3 pin 11. Checking voltage directly at the wire on the back of the connector still returns only a few mV. I have validated that all fuses are healthy and I've run out of troubleshooting ideas. I'm afraid I have a bad ECM...
I've read through dozens of threads on this site and others, but don't know where to go from here. Looking for some suggestions or confirmation that I indeed have a bad ECM. Please ask if you need info that I have failed to provide. Thanks in advance!
Build details if interested (or applicable) :
2005 LH6 Alum 5.3 w/E40 ECM
.020 over bore w/new HE pistons/rings/rotating assembly balanced
BTR Truck Cam v2 Stage 2
Speed Engineering headers
Single high-flow cat
Bank 2 O2 deleted
4l60e Monster rebuild
HP Tuners MPVI2 Pro
AEM Wideband
Thread Starter
Teching In
Joined: Aug 2021
Posts: 7
Likes: 0
Thanks Thank you for the prompt reply and apologies for the delay in my response (family issues)
I have studied several documents, including the pinout of the E40 ECM and the wiring diagram for the MAF/IAT sensor. (Links to both below)
MAF/IAT diagram - https://www.tbssowners.com/threads/i...06-tbss.36253/
E40 Pinout - https://www.pcmofnc.com/install/E40%20pinout.pdf
It seems that C3 Pin 11 should be providing 5v. Unfortunately, mine is not. The harness is nearly stock with the exception of a 3 relay efan. I de-pinned the wires for the PWM clutch fan and modified them to run the relays for the efans. There was a 5v reference as part of clutch fan harness, but it seemed to be direct to the clutch fan harness. I will try to trace the wire again to be certain.
PWM clutch fan diagram - https://www.trailvoy.com/threads/wir...ng-fan.205041/
I have studied several documents, including the pinout of the E40 ECM and the wiring diagram for the MAF/IAT sensor. (Links to both below)
MAF/IAT diagram - https://www.tbssowners.com/threads/i...06-tbss.36253/
E40 Pinout - https://www.pcmofnc.com/install/E40%20pinout.pdf
It seems that C3 Pin 11 should be providing 5v. Unfortunately, mine is not. The harness is nearly stock with the exception of a 3 relay efan. I de-pinned the wires for the PWM clutch fan and modified them to run the relays for the efans. There was a 5v reference as part of clutch fan harness, but it seemed to be direct to the clutch fan harness. I will try to trace the wire again to be certain.
PWM clutch fan diagram - https://www.trailvoy.com/threads/wir...ng-fan.205041/
Thread Starter
Teching In
Joined: Aug 2021
Posts: 7
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Another prompt response, thank you so much!
Sorry for the confusion in my reply regarding MAF power. I have confirmed that the fuse is good, I have checked voltage at Pin D to body ground as well as to Pin C. With Key on/engine off AND engine running, always get clean 12+ volts. I checked the Ohms on Pin C to body ground and Batt Neg and it's clean with nearly 0 ohms.
The only inconsistency I have is the MAF Signal does not have 5v. I won't be able to trace the 5v ref I mentioned above until this evening at the earliest, but will check back when I do. Unless that 5v reference is somehow spliced into the MAF signal wire, it seems that the PCM should be providing the 5v direct to MAF. That's what has me concerned the PCM may be at issue.
Sorry for the confusion in my reply regarding MAF power. I have confirmed that the fuse is good, I have checked voltage at Pin D to body ground as well as to Pin C. With Key on/engine off AND engine running, always get clean 12+ volts. I checked the Ohms on Pin C to body ground and Batt Neg and it's clean with nearly 0 ohms.
The only inconsistency I have is the MAF Signal does not have 5v. I won't be able to trace the 5v ref I mentioned above until this evening at the earliest, but will check back when I do. Unless that 5v reference is somehow spliced into the MAF signal wire, it seems that the PCM should be providing the 5v direct to MAF. That's what has me concerned the PCM may be at issue.
Look at that diagram. See how the MAF is getting 12v power from the ENG SENS fuse? That's a 12v sensor.
Now look at the MAP. See how its getting a 5v reference power from the PCM? That's a 5v sensor.
If you aren't getting any voltage on the MAF circuit that means the MAF isn't reading. Even if the MAF is disabled in the tune, I believe it's still going to read voltage because air is moving across the element, the PCM is just going to ignore it.
If I have misunderstood your problem regarding a 5v issue I apologize.
Now look at the MAP. See how its getting a 5v reference power from the PCM? That's a 5v sensor.
If you aren't getting any voltage on the MAF circuit that means the MAF isn't reading. Even if the MAF is disabled in the tune, I believe it's still going to read voltage because air is moving across the element, the PCM is just going to ignore it.
If I have misunderstood your problem regarding a 5v issue I apologize.
Actually I think I have. I went back and reread your original post and I believe I misunderstood it.
I'll delete my posts so I don't dedrail your thread anymore than I already have.
My apologies.
I'll delete my posts so I don't dedrail your thread anymore than I already have.
My apologies.
If you are getting power and ground to the MAF, and the MAF isn't outputting any voltage to the PCM. I would lean towards the MAF being bad. Not the PCM.
Is the IAT sensor reading correctly?
If the MAF isn't reading, you should be getting some DTC's
Is the IAT sensor reading correctly?
If the MAF isn't reading, you should be getting some DTC's
Thread Starter
Teching In
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IAT Seems to be working well. Temp is variable and goes up when engine is up to temp. I definitely have DTCs as well as no MAF values in HPT when engine is running. Both with current MAF and replacement from AutoZone.
If I understand the MAF circuit correctly (and there is a strong chance that I don't), it seems that the PCM is what generates the 5v, not the MAF. According to the troubleshooting doc that I linked in OP, with the MAF disconnected and ignition on, you should read 5v on Pin E (Yellow wire).
https://ls1tech.com/forums/pcm-diagn...tml#post331560
This is the location that I read only a few mV. At the connector and on the back of the C3 pin 11 connector at the PCM. I also Ohm'd the yellow wire and get 0 ohms, so it doesn't seem to have a break.
Sorry for the back and forth and thanks again for attempting to assist. It is truly appreciated!
If I understand the MAF circuit correctly (and there is a strong chance that I don't), it seems that the PCM is what generates the 5v, not the MAF. According to the troubleshooting doc that I linked in OP, with the MAF disconnected and ignition on, you should read 5v on Pin E (Yellow wire).
Step 5
1) Turn OFF the ignition.
2) Disconnect the MAF sensor connector.
3) Turn ON the ignition leaving the engine OFF.
4) Measure the voltage between the MAF sensor signal circuit and the battery ground using the DMM J 39200 . Refer to Measuring Voltage in Wiring Systems.
Is the voltage near the specified value?
Specified Value = 5V
1) Turn OFF the ignition.
2) Disconnect the MAF sensor connector.
3) Turn ON the ignition leaving the engine OFF.
4) Measure the voltage between the MAF sensor signal circuit and the battery ground using the DMM J 39200 . Refer to Measuring Voltage in Wiring Systems.
Is the voltage near the specified value?
Specified Value = 5V
This is the location that I read only a few mV. At the connector and on the back of the C3 pin 11 connector at the PCM. I also Ohm'd the yellow wire and get 0 ohms, so it doesn't seem to have a break.
Sorry for the back and forth and thanks again for attempting to assist. It is truly appreciated!
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IAT Seems to be working well. Temp is variable and goes up when engine is up to temp. I definitely have DTCs as well as no MAF values in HPT when engine is running. Both with current MAF and replacement from AutoZone.
If I understand the MAF circuit correctly (and there is a strong chance that I don't), it seems that the PCM is what generates the 5v, not the MAF. According to the troubleshooting doc that I linked in OP, with the MAF disconnected and ignition on, you should read 5v on Pin E (Yellow wire).
https://ls1tech.com/forums/pcm-diagn...tml#post331560
This is the location that I read only a few mV. At the connector and on the back of the C3 pin 11 connector at the PCM. I also Ohm'd the yellow wire and get 0 ohms, so it doesn't seem to have a break.
Sorry for the back and forth and thanks again for attempting to assist. It is truly appreciated!
If I understand the MAF circuit correctly (and there is a strong chance that I don't), it seems that the PCM is what generates the 5v, not the MAF. According to the troubleshooting doc that I linked in OP, with the MAF disconnected and ignition on, you should read 5v on Pin E (Yellow wire).
https://ls1tech.com/forums/pcm-diagn...tml#post331560
This is the location that I read only a few mV. At the connector and on the back of the C3 pin 11 connector at the PCM. I also Ohm'd the yellow wire and get 0 ohms, so it doesn't seem to have a break.
Sorry for the back and forth and thanks again for attempting to assist. It is truly appreciated!
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Teching In
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Just got the car put back together. Pulled engine/trans for full rebuild with cam upgrade. It runs fine, but was just starting to dig into the tune. Watched a ton of YouTube videos for HPTuners MAF tune and discovered that mine wasn't working. Hadn't cleared the DTCs since I fired without the MAF connected and so thought it was an old warning.
Worst case scenario, I could go speed density, but was hoping to keep it simple. SD is beyond my skillset for now. Will take a lot more research.
Worst case scenario, I could go speed density, but was hoping to keep it simple. SD is beyond my skillset for now. Will take a lot more research.
