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240 1990 245 lh 2.4 code 123 after replacing ECT sensor

prometheus_aflame

New member
Joined
Oct 21, 2015
Location
Chattanooga, TN
I have a friend who has a 1990 245 DL that threw a code 123 on the lh 2.4 diagnostic, indicating a missing or faulty ECT sensor signal. The sensor on there was badly corroded, so I replaced it with a new Bosch one from FCP Euro. After replacement, the ECU was reset and the same code is being thrown. At this time, we know that the water pump is bad and it's about to get replaced. Could a bad water pump cause a stalling condition in this scenario? The coolant temp gauge in the cluster is not going above halfway at full throttle. Current symptoms are a diving idle at stop and intermittent stalling at stop, but not while the car is moving. Fuel Pump Relay is engaging and the main pump is not straining. Throttle response is good after replacing the air filter with an iPD panel filter. What gives? Bad ground? Bad sensor wire?

If anyone has a testing procedure that I can follow, please share. Thanks.
 
Did you replace the sensor with just a single wire on it? Located under the manifold around number two cylinder? That is the one for the gauge but has no interface with the computer. The sensor for the computer is further back on the cylinder head and has a two wire connector. You can test by removing the ecu and icu and checking the resistance to the sensor. These can also get corroded connections. But first start with the correct sensor which is only used by the computers and not the gauge.
 
Code 123 would have almost nothing to do with the coolant level or anything to do with that except for temp.

Also backprobe pin 5 on the LH ECU connector, that should be a nice clean ground, if not check the manifold connections, and where the grounds all join together under the manifold.

Because it is easy to swap the connectors, make sure that the wrong one didn't get put on (Knock sensor, cold start, ECT, and I think the IAC all use the Bosch EV1 connector)

I have battled a 123 code on my car for a while, thinking it was this or that, seems like my harness has an intermittent ground issue causing problems. That was a tough one to figure out because there is nothing in the diagrams that show a ground for the ECT circuit really.
 
Did you replace the sensor with just a single wire on it? Located under the manifold around number two cylinder? That is the one for the gauge but has no interface with the computer. The sensor for the computer is further back on the cylinder head and has a two wire connector. You can test by removing the ecu and icu and checking the resistance to the sensor. These can also get corroded connections. But first start with the correct sensor which is only used by the computers and not the gauge.

I replaced the two-wire sensor under the #3 cylinder, right next to the cold start valve. That sensor wire connector is a bit tough to reach without removing the intake manifold, so I removed the intake hoses and all of the IAC valve hoses with the IAC bracket to gain access. I used a deep well 19mm socket attached to a U-Joint extension, and then removed it after attaching another deep well extension so I could get enough space to turn the ratchet for removal and assembly.

I used this video as a guide, but removed the intake components rather than the ignition components to gain access. I also didn't drain the coolant:

https://www.youtube.com/watch?v=4q8SeMlQ-G8

I would like to note that this issue did not start until after I replaced the thermostat. I am going to check the thermostat position to ensure it didn't shift under the thermostat housing.

The ect sensor I used is the one in the URL below, Bosch part number 0280130032:

https://www.fcpeuro.com/products/porsche-volvo-engine-temperature-sensor-0280130032

It is the IAT sensor mounted near the number 3 cylinder and has a two-wire connection. I made sure prior to starting the replacement.

@Uncleknuckklez I have given the owner instructions in advance to clean all of the grounds everywhere in the engine bay in advance of starting this thread.

I need a link or a reference to all of the ground locations under the hood. Can a contributor provide this info in this thread, please?
 
have you checked the wiring between ECT and ECU? continuity, clean uncorroded connections.
don't know if it is the same deal on the 240 but on LH2.4 7/9's there are large wiring loom connectors behind the strut towers. sometimes there is corrosion inside those connectors.
 
After reading your post. I would second the suggestion that you may have swapped the wrong connector onto the sensor. Also make sure the wiring is ok. The engine coolant temp sensor gets it's ground throgh the threads of the sensor. So if you put teflon tape or some other insulator on the threads. Then you may be blocking the ecu and icu from reading the sensor since it won't be grounded.
 
I disconnected two of the sensor wires during this job, which are the IAC valve connector and the ECT sensor connector. I am not getting code 223, which references no signal from the IAC valve, only code 123. I marked the connectors during disassembly to ensure they were reassembled correctly. Code 223 references a low idle consistently and very difficult starting, which is not happening in this case. The IAC valve is also new.

I'm heading up to Sewanee, TN to help the owner this week. I'm going to start by cleaning the grounds and go from there. I'll share photos in my next post.
 
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Measure resistance at the ECU plug. Open it and back probe. Wiggle test too.

Measure new and old sensor. From pin to BODY of sensor on 2.4.

Drag test and inspect terminals. Corrosion!? I "string" new circuits on modern cars all the time. Resistance test between each sensor terminal and the corresponding LH/Ezk terminal. This will require a good meter, some long leads, wiring diagram, and test terminals (I use needle probes, but best practice is the correct Male terminal). Front probing terminals with your meter is a rookie move. On modern cars you can't even stuff a meter lead down most connectors. Fine. It damages terminals!!!



Make sure that's the correct sensor! Do rez tests, as I said,. 2.4 uses rez between each pin to GROUND. (SENSOR BODY) 2.2 is rex between the two pins!!
 
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Update.

I cleaned the following grounds and applied dielectric grease to each:

-Firewall to valve cover
-Battery terminal wires to block near power steering pump.
-Negative battery terminal ground under the power steering reservoir

Resistance on the O2 sensor was off the charts (above 2 ohms). Replaced O2 sensor with a new one and applied dielectric grease to wiring harness connectors. The culprit was the MAF. The K&N filter melted oil off of the filter and splattered all over the airbox and MAF. I replaced the K&N filter with a new iPD high flow panel filter. I also replaced the MAF with a tested functional spare.

Started up the car, and voila! The interior lights are twice as bright, and no more stalling, no codes after 30 minutes of driving.
 
Gives you a different perspective on "high flow" air filters.
-L

That's for sure. The iPD air filter is not oiled, so no MAF death risk this time. Simple cleaning with soap and water when dirty. I'm dumping K&N filters permanently. Nothing but trouble.

I should also add that I cleaned up the airbox and the MAF inlet hose from the airbox to the MAF thoroughly with carb cleaner. I let it dry for about an hour prior to assembly and wiped it all down with a shop towel. Cleaned up the spare MAF with MAF cleaner and dropped dielectric grease on the electrical mating surface.
 
Update. The code 123 has recurred. I am progressing with wiring troubleshooting at this stage. The code is not thrown until the engine is running for a few minutes. Stalling at deceleration is the current symptom. Will update once all the wiring tests are done.
 
I too have chased this problem. It's not fun. On my 240, I replaced the connectors and the wires back to the fuel and ignition computers. A good 3 foot section was corroded. That seemed to do the trick. The insulation looked completely solid and new, but the copper inside had suffered from years of heating and cooling/ condensing cycles. I would definitely try to diagnose properly before one goes hacking away. Here is a pin out if this helps for testing: https://drive.google.com/open?id=1xLqOhXVTF0NbScQS6-oFW_29F-40ejZRYuXe0eKSlnM

Here is the ECT values as well if you need them:
[url=https://postimg.cc/0rXJpMNJ][/URL]

Good luck!
 
I was surprised to hear a claim cleaning grounds or swapping MAF fixed an ECT code. I was gonna reply, but was waiting for the "code came back" post.

I fix electrical problems on modern cars with very sensitive electronics.

If you know the sensor is good, I would probably just go ahead and "re-string the circuit". You said the connector was oxidized!!! I bet the wiring is green inside the crimps.

Locate new terminals. I think Dave Barton sells them. And run new wiring. New terminals at the ECU too. Its advanced work, but that's how we do it professionally to prevent a comeback. You just got a comeback!

If you wanna take a shortcut, snip a good terminal off a donor car or get one here. Then solder and heat shrink new wires to it, run new wire all the way to the EZK and the LH box. Solder and heat shrink. No butt connectors!! Those cause too much resistance and can cause codes to come back.

If you have replaced the sensor and wiring. The final step would be to swap the computer that's throwing the code.
 
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I've been out west, sorry for the delay.

The stalling issue was finally corrected. I found a spark plug that was arcing. Replaced all the plugs and sprayed the plug wire contact points with deoxit, then lubed the boots with dielectric grease. It's still throwing code 123 and running crazy rich (10 MPG or so). I can't find any wiring faults on the harness or at the ECU. However, I DID find a bad ground to the alternator. I'm waiting on the owner to get that replaced and hoping that the harness isn't toast.
 
Alt ground wire isn't gonna fix it. That could be diagnosed with a voltage drop test. Look up how to do it.

I still recommend you put a new connector on the sensor and run two new wires as far as you can to each computer.

You also need to do resistance tests at each computer. I would do this before and after the repair to confirm. I would first unplug each computer, find the correct terminal, front probe with the proper test equipment, and measure for less than 2 ohms between the computer end of the wire and the sensor end of the wire. Is this too much work? It would also be wise to measure the resistance between each pin at the computer and ground.
 
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I recently bought a brand new sensor for my 93 wagon which is LH2.4 and the sensor was bad. So that resistance check will help you sort it out. The sensor caused the code right after replacemt. Put in a known good used one and it's fixed. I checked the sensor itself and it isn't the correct cnfiguration to work on LH2.4. The two pins had resistance together and were open to ground. The LH2.4 sensor is two sensor circuits that go to the body of the sensor as ground.
My bad as I should have checked the new part before I even put it in.
 
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