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Since I was last on here with a question, I have replaced my MAF Sensor with the correct one. This has corrected my MAT/INT AIR TEMP problem and has given me an accurate temp reading. But I am still getting a Code 34 MAF Sensor Low error.
One thing I have noticed on the Expertec Tech 1 codes is where it shows the actual MASS AIR FLOW reading, it has AIRFLOW 6 g/s. Although the MASS AIR FLOW will change with acceleration, the AIRFLOW will remain at 6 g/s. There was no manual in the box with the scanner, so I am not sure if that is a set point or if I have another problem to address.
This is the scanner I am using.
This is what I am questioning.... Not sure if this (or why) I am still getting a Code 34 MAF SENSOR LOW.
With acceleration, the flow increased to14.5 g/s, but the AIRFLOW still indicates 6 g/s.
Can anyone guide me to a resolution to my nuisance CODE 34??? What is MAF SENSOR LOW actually mean?
When a MAF error is present, the default airflow calculation will replace the mass airflow signal obtained from the sensor (subject to filtering and limitations) (16 bit signal).
The unlimited airflow signal is not replaced by the default airflow calculation and may no longer be updated once a MAF error code is set. I don't know if I have any data handy to demonstrate/confirm this effect.
On your scanner I think you are seeing the default airflow (calculated value) reported as: MASS AIR FLOW (which is varying with rpm) and the unlimited airflow value reported as: AIRFLOW (which is fixed at 6 gm/sec).
For an analog MAF, Code 34 is set if the MAF voltage is < 7 a/d counts (or < 0.140 volts). For a digital MAF, Code 34 is set if there is no signal for 6.4 seconds. Some say that 85 cars have a digital maf, but I'm skeptical of this. The software and hardware can support both sensor types (at least for 1986-1988 cars).
6 gm/sec would be about 0.00 volts (if using a 305 bin like APYS), or about 0.090 volts (if using a 350 bin). Both of which are less than the 0.140 volt threshold, so this value is consistent with the Code 34 failure detection settings.
Note: if the sensor signal wire was shorted to ground you would expect to see either 6 gm/sec or 8 gm/sec on the unlimited airflow signal depending upon the maf table calibration. An open circuit would show 255 gm/sec on the unlimited airflow signal and cause a Code 33 to be set instead.
What mask/bin/bcc are you running in the ecm? Has the programming been modified or tuned in any way?
Which ecm pin is your MAF sensor signal actually connected to? The input circuitry is different for analog and digital signals. Was the ecm or harness ever re-pinned/re-wired?
Analog MAF should be pin B12. Digital MAF should be pin B6.
Excerpt from 87-88 $32B code for reference:
;--------------------------------------------------------
; ERR 34 Params. Params, TYPE 32 ECM
; >> MAF Sensor Lo <<
;--------------------------------------------------------
LC216 FCB 40 ; 6.4 SEC'S, MIN TIME W/O SIGNAL, (IF FM DIG MAF), set ERR 34
LC217 FDB 0049 ; IF Analog CTS * 7 or PERIOD < this set ERR 34B
LC219 FCB 10 ; 1 Sec ERR #34B Min time req.
LC21A FCB 24 ; If RPM > 600, Ck ERR #34
LC21B FCB 16 ; If TPS > 6.25%, Ck ERR #34
LC21C FCB 0 ; If LV8 >= 0, Ck ERR #34
LC21D FCB 130 ; If LV8 <= 130, Ck ERR #34
LC21E FDB 0049 ; IF Analog CTS * 7 or PERIOD <, set ERR 34A
;--------------------------------------------------------
Last edited by tequilaboy; Oct 31, 2024 at 12:29 PM.
When a MAF error is present, the default airflow calculation will replace the mass airflow signal obtained from the sensor (subject to filtering and limitations) (16 bit signal).
The unlimited airflow signal is not replaced by the default airflow calculation and will still reflect the raw signal value obtained from the sensor (8 bit signal), or may no longer be updated once a MAF error code is set. I don't know if I have any data handy to demonstrate/confirm this effect.
On your scanner I think you are seeing the default airflow (calculated value) reported as: MASS AIR FLOW (varying with rpm) and the unlimited airflow value reported as: AIRFLOW (fixed at 6 gm/sec).
For an analog MAF, Code 34 is set if the MAF voltage is < 7 a/d counts (or < 0.140 volts). For a digital MAF, Code 34 is set if there is no signal for 6.4 seconds. Some say that 85 cars have a digital maf, but I'm skeptical of this. The software and hardware can support both sensor types (at least for 1986-1988 cars).
6 gm/sec would be about 0.090 volts (which is less than the 0.140 volt threshold), so this value is consistent with the Code 34 failure detection settings.
Note: if the sensor signal wire was shorted to ground you would expect to see 8 gm/sec not 6 gm/sec (on the unlimited airflow signal). An open circuit would show 255 gm/sec (on the unlimited airflow signal) and cause a Code 33 to be set.
What mask/bin/bcc are you running in the ecm? Has the programming been modified or tuned in any way?
Which ecm pin is your MAF sensor signal actually connected to? The input circuitry is different for analog and digital signals. Was the ecm or harness ever re-pinned/re-wired?
Analog MAF should be pin B12. Digital MAF should be pin B6.
Excerpt from 87-88 $32B code for reference:
;--------------------------------------------------------
; ERR 34 Params. Params, TYPE 32 ECM
; >> MAF Sensor Lo <<
;--------------------------------------------------------
LC216 FCB 40 ; 6.4 SEC'S, MIN TIME W/O SIGNAL, (IF FM DIG MAF), set ERR 34
LC217 FDB 0049 ; IF Analog CTS * 7 or PERIOD < this set ERR 34B
LC219 FCB 10 ; 1 Sec ERR #34B Min time req.
LC21A FCB 24 ; If RPM > 600, Ck ERR #34
LC21B FCB 16 ; If TPS > 6.25%, Ck ERR #34
LC21C FCB 0 ; If LV8 >= 0, Ck ERR #34
LC21D FCB 130 ; If LV8 <= 130, Ck ERR #34
LC21E FDB 0049 ; IF Analog CTS * 7 or PERIOD <, set ERR 34A
;--------------------------------------------------------
You can see that the maf unlimited airflow and mass air flow signals are tracking with each other prior to 273.5 seconds. Once the error occurs, the unlimited airflow signal remains fixed high (at 49 gm/sec in this case), while the mass airflow signal continues to vary with tps and rpm. This is the default airflow calculated signal in action after 273.5 seconds (and the actual mass air flow signal prior to 273.5 seconds).
It takes another 5 seconds for the Code 33 flag to go from OK to Error.
Note: this car shows a huge discrepancy between the actual mass air flow signal and the default air flow calculation. The two values differ by about 20 gm/sec. This car likely has had modifications which contribute to the default air flow calculation error or has an inflated maf calibration. It could benefit from some tuning.
;--------------------------------------------------------
; ERR 33 Params, TYPE 32 ECM
; >> MAF Sensor Hi <<
;--------------------------------------------------------
LC210: FCB 38 ; If TPS >= 14.8%, disable ERR #34
LC211: FCB 45 ; If Air Flow GT 45 gms/sec, SET ERR #33
LC212: FCB 96 ; If > 6 sec, Set code ERR 33, (Num + Arg * 16) /*. note: appears to be 6 seconds not 600 ms as was originally commented corrected values shown .*/
LC213: FCB 10 ; 1000 msec, ERR #33 Min time req. (Num = Arg * 10)
LC214: FCB 128 ; If RPM > Disable ERR 33, (TBL1, NTRPM) 2200 RPM
LC215: FCB 100 ; If Pump Volts <= 10 vdc, Bypass ERR 33
;--------------------------------------------------------
Code 34 would be expected to behave in a similar manner but with the signals reversed (the unlimited airflow should remain fixed to a low value, while the mass air flow signal will continue to function via the default airflow calculation as shown by your scan tool).
Last edited by tequilaboy; Oct 14, 2024 at 10:45 PM.
Still experiencing the same problem. No vacuum leaks. System is entirely new. Check engine light comes on whether idling and kicking down the accelerator, or driving and doing the same. Took the filter off entirely with the same results. Figured I'd ask the experts here before giving up and try to find a shop that has the ability to deal with the problem.
Back to Code 34: Is it failing immediately at startup (off throttle), or while running with the tps > 6.25 % and rp
No, only after revving it up or driving at speed and accelerating.
Note: 6.25 % tps is around 0.8 volts. 7.03 % tps is 0.88 volts from logging the tps load axis. I don't have exact data for 6.25%.
Do you have a huge vacuum leak, or a mis-adjusted tps sensor? Check the tps voltage with your scan tool.
No leak.
The TPS voltage is at .44 volts both with MAF Sensor plugged in and unplugged.
Do you get a code 33 as expected with the maf sensor unplugged?
No...still Code 34 after revving it up or driving at speed and accelerating.
I apologize for not responding sooner...was out of commission after a medical procedure. I appreciate the help you are giving. Might be easier to hire you and fly you here!!!
Mike
Last edited by mcb55-210; Oct 26, 2024 at 11:23 AM.
