E320 ECU and O2 sensors
#1
09-20-2017, 12:26 PM
E320 ECU and O2 sensors
I would like to share my experience with O2 sensor problemson my 1999 E320 sedan and hopefully save a lot of troubles and money to thefortunate readers that will end up reading this post…
Everything started with “Check Engine” light coming andstaying on. When diagnosed the ECU returned O2 sensor heater circuitmalfunction codes. Without doing my due diligence to thoroughly investigate theproblem, I purchased and replaced all 4 sensors with new aftermarket sensorsfrom “eccppautoparts” on EBay for$18.89 each – my first big mistake. Replacing the O2 sensors, more so theupstream ones on Mercedes E320 is not an easy task, especially if you don’thave the right tools, which I didn’t at the time. After suffering through thattask, I was surprised to see that the CEL (check engine light) came on again.Now I started reading and gaining more information on O2 sensors, emissioncontrol systems and ECUs (engine control unit or the car computer). Having moreinsight of the situation, I checked the wiring, connections, conductivity andresistance of the heater circuits of the O2 sensors. Everything checked OK andI excluded the O2 sensors as a source of the problem (which further worsened myfirst mistake). Now, confident that my sensors and electrical connections arefine, I went on to check the signals from the ECU to the sensors. Logically, Iwas starting to suspect the ECU itself. So while the +12V signal to the one endof the heater circuits was present on all 4 sensors, the ground signal from theECU was missing – on all of them. Here I made a second big mistake byconcluding that the ECU was defective. I was checking the signals from the ECUwhile the CEL was still on. I should’ve done that AFTER clearing the codes, butI learned that later. So now, thinking that I have a fried ECU, I searched theinternet for ECU repairs and for my worst luck ended up dealing with a companycalled CAR COMPUTER EXCHANGE. I was instructed to ship my ECU to them andthey’ll repair and ship back to me for the price of $300.00. I did that and waswaiting and waiting for the ECU to come back. Weeks passed by and I startedcalling CCE (Car Computer Exchange) to find out what is going on. They said theunit was heavily damaged and could not be repaired at first attempt, but theywill try again and let me know. More weeks passes before I called again and wastold this time that the unit is beyond repair and I have to bay a replacementunit for $500.00. Now, please remember that dealing with this company was byfar the worst experience of that nature in my life. This people are terrible andtheir goal is to rob your money at all cost. After refusing to buy areplacement unit from them I asked for the return of my original ECU. Was toldthat they’ll ship it back to me, but will charge me $150.00 for the “work” theyhave done. I was very mad – my car was sitting for more than a month – butagreed. After all the car was running just fine with the original ECU, just theCEL was on. When the unit finally came back, I installed it in the car,attempted to start the car and… nothing. The car won’t crank at all. The ECUwas totally dead. Then started my long and painful hurdle with Car ComputerExchange. They insisted that my ECU was bad and beyond repair, which laterproved not to be the case at all. These people are liars and they don’t knowwhat they are doing. I filed a complaint with BBB which is titled “CAR COMPUTEREXCHANGE destroyed my ECU and charged me $150.00 to do so.” I also posted somereviews for this company, but that’s beside the point here.
So at this point my car was dead, I couldn’t drive it to ashop or the dealer and the dealer by the way estimated the repair at around $4,000.00!The whole car is barely worth that much providing everything works!
Next, I tried installing different used ECU and that didn’twork of course since the ECU is programed for a specific car and key and is notinterchangeable!
I ended up buying the complete set from another car – thekey, the key electronic module, the steering column lock mechanism and the ECU.Cost me ~$250.00 from EBay. Replacing the steering column lock is hard, therest is not so bad.
Having everythinginstalled, the car started again and was running fine. The CEL was off, butafter driving the car for short while, it came on. The diagnostic codes wereagain for the O2 sensors – P0135, P0155, P0141 and P0161 – O2 sensor heatercircuit malfunction.
At this point Irealized that I have overlooked something when checking and investigating theO2 sensors. I checked the signals from the ECU again, this time AFTER CLEARINGTHE ERROR CODES. I was getting +12V and the ground signal at the heatercircuits. I actually connected a small 12V light bulb to the ends that supposedto supply the heater element. When I turned the key to ON position, the lightbulb went ON. The ECU was attempting to operate the sensor. Obviously, theproblem WAS NOT IN THE ECU. I was reading more and more articles on O2 sensorsand ECUs and their principles of operation. Some of them were so detailed as togo to electron’s level of operation. I learned that the ECUs are very picky onwhat kind of O2 sensors they can accept and will bitch if you try to usedifferent ones. They read the response time of the sensors once the heatercircuit has been activated and will generate error code if the response time islonger than expected. Well, obviously the heater element will reach certaintemperature faster if the resistance of the element is lower and vice-versa. Sonow I re-measured the heater circuit of the sensors this time paying attentionof the actual value, not only whether there is open or short circuit. The O2sensors that I purchased from “eccppautoparts” had resistance of 9 - 10 ohms vs2-3 ohms of the OEM sensors. And that’s probably only one of many issues withthese aftermarket sensors.
OK, so I purchased and installed (with the right tools thistime) OEM sensors, cleared the codes and started the car. Drove it for 2 weeks– all fine. The CEL stayed off, no codes of any kind. The car passed theemission control test and I’m commuting with it every day now. The wholeproblem after all was in the O2 sensors. The ECU was fine altogether and thatshould be the very last thing someone shouldsuspect.
Finally, besides my obvious mistakes I want to make youaware of these two companies:
CAR COMPUTER EXCHANGE – avoid dealing with them at any cost.
Eccppautoparts onEBay – they are selling aftermarket garbage.
Everything started with “Check Engine” light coming andstaying on. When diagnosed the ECU returned O2 sensor heater circuitmalfunction codes. Without doing my due diligence to thoroughly investigate theproblem, I purchased and replaced all 4 sensors with new aftermarket sensorsfrom “eccppautoparts” on EBay for$18.89 each – my first big mistake. Replacing the O2 sensors, more so theupstream ones on Mercedes E320 is not an easy task, especially if you don’thave the right tools, which I didn’t at the time. After suffering through thattask, I was surprised to see that the CEL (check engine light) came on again.Now I started reading and gaining more information on O2 sensors, emissioncontrol systems and ECUs (engine control unit or the car computer). Having moreinsight of the situation, I checked the wiring, connections, conductivity andresistance of the heater circuits of the O2 sensors. Everything checked OK andI excluded the O2 sensors as a source of the problem (which further worsened myfirst mistake). Now, confident that my sensors and electrical connections arefine, I went on to check the signals from the ECU to the sensors. Logically, Iwas starting to suspect the ECU itself. So while the +12V signal to the one endof the heater circuits was present on all 4 sensors, the ground signal from theECU was missing – on all of them. Here I made a second big mistake byconcluding that the ECU was defective. I was checking the signals from the ECUwhile the CEL was still on. I should’ve done that AFTER clearing the codes, butI learned that later. So now, thinking that I have a fried ECU, I searched theinternet for ECU repairs and for my worst luck ended up dealing with a companycalled CAR COMPUTER EXCHANGE. I was instructed to ship my ECU to them andthey’ll repair and ship back to me for the price of $300.00. I did that and waswaiting and waiting for the ECU to come back. Weeks passed by and I startedcalling CCE (Car Computer Exchange) to find out what is going on. They said theunit was heavily damaged and could not be repaired at first attempt, but theywill try again and let me know. More weeks passes before I called again and wastold this time that the unit is beyond repair and I have to bay a replacementunit for $500.00. Now, please remember that dealing with this company was byfar the worst experience of that nature in my life. This people are terrible andtheir goal is to rob your money at all cost. After refusing to buy areplacement unit from them I asked for the return of my original ECU. Was toldthat they’ll ship it back to me, but will charge me $150.00 for the “work” theyhave done. I was very mad – my car was sitting for more than a month – butagreed. After all the car was running just fine with the original ECU, just theCEL was on. When the unit finally came back, I installed it in the car,attempted to start the car and… nothing. The car won’t crank at all. The ECUwas totally dead. Then started my long and painful hurdle with Car ComputerExchange. They insisted that my ECU was bad and beyond repair, which laterproved not to be the case at all. These people are liars and they don’t knowwhat they are doing. I filed a complaint with BBB which is titled “CAR COMPUTEREXCHANGE destroyed my ECU and charged me $150.00 to do so.” I also posted somereviews for this company, but that’s beside the point here.
So at this point my car was dead, I couldn’t drive it to ashop or the dealer and the dealer by the way estimated the repair at around $4,000.00!The whole car is barely worth that much providing everything works!
Next, I tried installing different used ECU and that didn’twork of course since the ECU is programed for a specific car and key and is notinterchangeable!
I ended up buying the complete set from another car – thekey, the key electronic module, the steering column lock mechanism and the ECU.Cost me ~$250.00 from EBay. Replacing the steering column lock is hard, therest is not so bad.
Having everythinginstalled, the car started again and was running fine. The CEL was off, butafter driving the car for short while, it came on. The diagnostic codes wereagain for the O2 sensors – P0135, P0155, P0141 and P0161 – O2 sensor heatercircuit malfunction.
At this point Irealized that I have overlooked something when checking and investigating theO2 sensors. I checked the signals from the ECU again, this time AFTER CLEARINGTHE ERROR CODES. I was getting +12V and the ground signal at the heatercircuits. I actually connected a small 12V light bulb to the ends that supposedto supply the heater element. When I turned the key to ON position, the lightbulb went ON. The ECU was attempting to operate the sensor. Obviously, theproblem WAS NOT IN THE ECU. I was reading more and more articles on O2 sensorsand ECUs and their principles of operation. Some of them were so detailed as togo to electron’s level of operation. I learned that the ECUs are very picky onwhat kind of O2 sensors they can accept and will bitch if you try to usedifferent ones. They read the response time of the sensors once the heatercircuit has been activated and will generate error code if the response time islonger than expected. Well, obviously the heater element will reach certaintemperature faster if the resistance of the element is lower and vice-versa. Sonow I re-measured the heater circuit of the sensors this time paying attentionof the actual value, not only whether there is open or short circuit. The O2sensors that I purchased from “eccppautoparts” had resistance of 9 - 10 ohms vs2-3 ohms of the OEM sensors. And that’s probably only one of many issues withthese aftermarket sensors.
OK, so I purchased and installed (with the right tools thistime) OEM sensors, cleared the codes and started the car. Drove it for 2 weeks– all fine. The CEL stayed off, no codes of any kind. The car passed theemission control test and I’m commuting with it every day now. The wholeproblem after all was in the O2 sensors. The ECU was fine altogether and thatshould be the very last thing someone shouldsuspect.
Finally, besides my obvious mistakes I want to make youaware of these two companies:
CAR COMPUTER EXCHANGE – avoid dealing with them at any cost.
Eccppautoparts onEBay – they are selling aftermarket garbage.
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