94 E420 keep getting code 3

[DRICHFL]

For the last several months I have been getting Check Engine light. I have been doing the quick push button under the hood and keep getting 3 flash. I reset and have replace the O2 Sensor twice. I still get the CEL and same 3 flashes. What is going on. Plz help, I gonna take the time to scan all the modules when I have the time. Am I'm correct to replace O2 sensors.

[pesuazo]

A code 3 on the diagnostic module (Pin 19 or push button LED):
Lambda control inoperative Test LH-SFI unit

A code 3 on the diagnostic module does not necessarily mean it is the O2 sensor. A code 2 would.

You need to build the code reader an check Pin 4 for codes, this will narrow down the issue.

Codes for Pin 19 (the same as the push button LED):
1 No Faults in System -
2 Heated oxygen sensor inoperative Test LH-SFI unit
3 Lambda control inoperative Test LH-SFI unit
4 Air injection inoperative Test LH-SFI unit
5 Exhaust gas recirculation inoperative Test LH-SFI unit
6 Idle speed control inoperative Test electronic accelerator
7 Ignition system defective Test distributor igntion system
8 Engine coolant temperature sensor, open/short Test LH-SFI unit
9 Intake air temperature sensor, open/short Test LH-SFI unit
10 Voltage at mass air flow sensor too high/low Test LH-SFI unit
11 TN-signal (rpm) at LH-SFI control module (N3/1) defective Test LH-SFI unit
12 Heated oxygen sensor heater, open/short circuit Test LH-SFI unit
13 Camshaft position sensor signal of ignition control module (N1/3) defective Test LH-SFI unit
14 Intake manifold pressure at start in N1/3 too low/high Test LH-SFI unit
15 Wide open throttle information defective Test LH-SFI unit
16 Closed throttle position information defective Test electronic accelerator
17 Data exchange malfunction between individual control modules Test DM Step: 7.0
18 Adjustable camshaft timing solenoid, open/short circuit Test LH-SFI unit
19 Fuel injectors open/short or self-adaptation in LH-SFI control module (N3/1) at limit Test LH-SFI unit and reset adaptation to mean value
20 Speed signal not present Test electronic accelerator
21 Purge switchover valve, open/short circuit Test LH-SFI unit
22 Camshaft position sensor signal defective Test distributor system
23 Intake manifold pressure in N1/3 with engine running too high/low Vacuum supply to N1/3; Test distributor ignition system
24 Start ring gear segments and/or crankshaft position sensor defective Test distributor system
25 Knock sensors or ignition control module defective Test distributor system
26 Upshift delay 1 to 2 (model 123.034) , 2 to 3 (all models) Test LH-SFI unit
27 Engine coolant temperature sensor deviation between sensor ckt 1 and sensor ckt 2 Test LH-SFI unit
28 Engine coolant temperature sensor (coolant temperature change monitor Test LH-SFI unit

[DRICHFL]

Pesuazo, thanks for your reply. I do have the code reader but I was just using the quick push button under the hood to get flash code. As you can see from what you posted Code #3 "Lambda control inoperative Test LH-SFI unit" is the O2 Sensor. However, my concern is that I continue to get the same code after reset and after replacing the so called bad sensor.

My thought is that my LH unit might be bad or has a glitch.

Has this happen to anyone else and was replacing the module the fix to this problem.

[pesuazo]

Sorry, I posted the wrong codes for Pin 4, below are the correct ones, I also updated my previous post;
The little LED is giving you a code 3, or asking you to check the LH-SFI unit (Codes for the LH-SFI unit come from Pin 4)

The LH-SFI ECU contains several programs and functions as described in the following:
- Voltage Supply (+12.5V)
- Starter circuit
- Engine temperature from coolant temperature sensor (B11/2)
- Intake air temperature from intake manifold temperature sensor (B17/7)
- Intake air mass from mass air sensor (B2/2)
- Various information from the controller area network (CAN)
- ABS/ASR information from ABS/ASR control module (N30/1)
- Air/fuel mixture from oxygen sensor (G3/2)
- ON signal from air injection
- ON signal for exhaust gas recirculation (EGR)


Socket 1: Black (Ground)
Socket 3: Red (+12.5V)
Socket 4: Yellow (Pin for LH-SFI DTC readout)

DTC Readout Possible Cause
1 No Faults in System
2 ECT sensor (B11/2) sensor circuit 1, open/short circuit
3 ECT sensor (B11/2) sensor circuit 2, open/short circuit
4 Voltage at hot wire MAF sensor (B2/2) insufficient or too high, or open circuit in ground wire at hot wire MAF sensor
5 Not used
6 Not used
7 TN-signal (rpm signal) incorrect or open/short circuit
8 CMP sensor (L5/1), open/short circuit
9 Starter signal (circuit 50) missing, open/short circuit
10 CTP (idle) recognition from EA/CC/ISC control module (N4/1), short circuit
11 Secondary air injection system, open/short circuit
12 Burn-off control for hot wire MAF sensor, open/short circuit
13 IAT sensor (B17/7), open/short circuit
14 Not used
15 Not used
16 EGR switchover valve (Y27), open/short circuit
17 No CAN data transmission with EA/CC/ISC control module (N4/1) or N4/3)
18 No CAN data transmission with DI control module (N1/3)
19 Not used
20 No CAN data transmission with LH-SFI control module (N3/1)
21 O2S 1 (before TWC) (G3/2), open/short circuit
22 O2S 1 heater, open/short circuit
23 Purge control valve (Y68/1), open/short circuit
24 Left adjustable camshaft timing solenoid (Y49/1), open/short circuit
25 Right adjustable camshaft timing solenoid (Y49/2), open/short circuit
26 Upshift delay switchover valve (Y3/3), open/short circuit
27 Injectors (Y62), open/short circuit
28 LH-SFI control module coding, open circuit
29 1GR start relay module (K29/1), open/short circuit

[mbdoc]

Since you are reading codes from the DM, diagnostic module on a M119 LH system...

Code #3 is all about fuel mixture.
Since the O2 sensor didn't fix that issue, then either fuel pressure OR air mass sensor is most likely the culprit.

[DRICHFL]

MBDOC and Pesuazo thanks guys I cleaned the Hot-Wire Air Mass Sensor and the ETA Buterfly which was really dirty. That did the trick no more CEL.

[pesuazo]

Nice and congrats...

Just for completion sake, check the codes at pin 4; It would be nice to know what codes you got there with a dirty hot wire MAF sensor.

I wish everyone also posted the solution to their problems...

[JimF]

Originally Posted by DRICHFL

MBDOC and Pesuazo thanks guys I cleaned the Hot-Wire Air Mass Sensor and the ETA Buterfly which was really dirty. That did the trick no more CEL.

Thanks for the new data-point re cleaning of the Hot-Wire MAF. It seems that the they can be successfully cleaned but the hot-film can't.

Menu #4 here gives some detail and results.

[DRICHFL]

Thanks Jimf, you have always giving us great insight on Benz.

[DRICHFL]

Well since I replaced the Rear Lower Control Arm Bushing I have been driving the E420 more often. The Dianostic Module push button DTC code 3 was back. I would drive the car and after three ignition starts the MIL/CEL was back on again. Push the button to pull the code under the hood and then reset. The Diagnostic Module (N59) DTC Code 3 "Lambda control inoperative" continue to reappear; in addition, my air compressor clutch stop engaging. The a/c clutch would engage for a few seconds then shut off at ignition start ups.

I would scan the LH-SFI Module (N3/1) and get DTC Code 4 "Voltage at hot wire MAF sensor (B2/2) insufficient or too high, or open circuit in ground wire at hot wire MAF sensor."


Each time I drive the car these codes were sure to appear.

SOLUTION TO THIS PROBLEM:
I replaced the LH-SFI Module and no more CEL. The a/c clutch problem was solved and it also solved my so-called over heating gauge problem.

I hope this help out some of the members that is having this issue.

[gerryvz]

Thanks for the update. Can you detail as to how you deduced it was the LH module?

Did you happen to try resetting the adaptation on your old LH unit before you replaced it?

Cheers,
Gerry


Sent from my iPhone using Tapatalk

[DRICHFL]

Gerry,

Yes indeed I have scan and reset the LH-SFI module (N3/1) several times. I still came up with the same DTC code 4 "Voltage at mass air sensor (MAF) with hot wire circuit insufficient or too high. Open or short circuit in ground wire."

-I pulled the MAF senor (B2/2) inspected the hot wire and it was fine.
-I remove the MAF wires connectors to see if there was any damage to the wires, all the wires were ok.
-Disconnect the ground wire from the MAF that is attach to the engine and i removed inspect the connection then reinstall, all the ground wires were ok.
-Removed the EGR switchover valve (Y/27) and clean it and reinstalled.
-Replace the Thermostat
-Replace the Coolant Temp Seneor (B11/2)
-Replace the Fan Switch on the engine also
-Replace the Base Module (16/1)

No change the vehicle continue to give me CEL.
-Replace the LH-SFI module (N3/1) and problems were solved.

I have drove this car about 500 miles, mostly highway, with no issue at this point but I will keep you posted if any arrives.