p1633 ECM / ETCS error on 98 ls400
#1
Driver School Candidate
Thread Starter
p1633 ECM / ETCS error on 98 ls400
Hello,
My brother was driving his 98 ls400 a couple days ago, when the check engine and vsc light on the car came on and the car seemed like it did not want to accelerate. I had to stop by to pick him up, but when i started the car a few minutes after this happened, it started and drove just fine. He stated that a few weeks ago, the car suddenly stopped accelerating for a quick second and started to work again. When i review the error codes on the car, the only error i see is p1633, which according to the service manual, is caused by a ram error, ecm cpu malfunction, or ETCS power supply malfunction. I believe all of these components are in the ecm, so is the ecm going bad?
It should also be noted that the car also has an issue with low idle. it idles around 400 rpm when warm, but if i turn on the ac or headlights, it goes up to ~600 rpm ( i think this car should idle around 700 rpm). A couple years ago, i changed all the spark plugs on the car, cleaned the throttle body and maf, and did the capacitor replacement on the ECM (the capacitors did not appear to be visually bad when i did this).
Any ideals on what could be going on? Thank you for looking.
PS: is there a way to troubleshoot or test an ECM, or is there a procedure for it at the techinfo site or service manual?
My brother was driving his 98 ls400 a couple days ago, when the check engine and vsc light on the car came on and the car seemed like it did not want to accelerate. I had to stop by to pick him up, but when i started the car a few minutes after this happened, it started and drove just fine. He stated that a few weeks ago, the car suddenly stopped accelerating for a quick second and started to work again. When i review the error codes on the car, the only error i see is p1633, which according to the service manual, is caused by a ram error, ecm cpu malfunction, or ETCS power supply malfunction. I believe all of these components are in the ecm, so is the ecm going bad?
It should also be noted that the car also has an issue with low idle. it idles around 400 rpm when warm, but if i turn on the ac or headlights, it goes up to ~600 rpm ( i think this car should idle around 700 rpm). A couple years ago, i changed all the spark plugs on the car, cleaned the throttle body and maf, and did the capacitor replacement on the ECM (the capacitors did not appear to be visually bad when i did this).
Any ideals on what could be going on? Thank you for looking.
PS: is there a way to troubleshoot or test an ECM, or is there a procedure for it at the techinfo site or service manual?
#2
BahHumBug
iTrader: (10)
Hello,
My brother was driving his 98 ls400 a couple days ago, when the check engine and vsc light on the car came on and the car seemed like it did not want to accelerate. I had to stop by to pick him up, but when i started the car a few minutes after this happened, it started and drove just fine. He stated that a few weeks ago, the car suddenly stopped accelerating for a quick second and started to work again. When i review the error codes on the car, the only error i see is p1633, which according to the service manual, is caused by a ram error, ecm cpu malfunction, or ETCS power supply malfunction. I believe all of these components are in the ecm, so is the ecm going bad?
It should also be noted that the car also has an issue with low idle. it idles around 400 rpm when warm, but if i turn on the ac or headlights, it goes up to ~600 rpm ( i think this car should idle around 700 rpm). A couple years ago, i changed all the spark plugs on the car, cleaned the throttle body and maf, and did the capacitor replacement on the ECM (the capacitors did not appear to be visually bad when i did this).
Any ideals on what could be going on? Thank you for looking.
PS: is there a way to troubleshoot or test an ECM, or is there a procedure for it at the techinfo site or service manual?
My brother was driving his 98 ls400 a couple days ago, when the check engine and vsc light on the car came on and the car seemed like it did not want to accelerate. I had to stop by to pick him up, but when i started the car a few minutes after this happened, it started and drove just fine. He stated that a few weeks ago, the car suddenly stopped accelerating for a quick second and started to work again. When i review the error codes on the car, the only error i see is p1633, which according to the service manual, is caused by a ram error, ecm cpu malfunction, or ETCS power supply malfunction. I believe all of these components are in the ecm, so is the ecm going bad?
It should also be noted that the car also has an issue with low idle. it idles around 400 rpm when warm, but if i turn on the ac or headlights, it goes up to ~600 rpm ( i think this car should idle around 700 rpm). A couple years ago, i changed all the spark plugs on the car, cleaned the throttle body and maf, and did the capacitor replacement on the ECM (the capacitors did not appear to be visually bad when i did this).
Any ideals on what could be going on? Thank you for looking.
PS: is there a way to troubleshoot or test an ECM, or is there a procedure for it at the techinfo site or service manual?
The following users liked this post:
BNastee (09-18-24)
#3
Moderator
There is no troubleshooting manual for the ECU. We need to analyse it all by ourselves or simply ask a dealership to fix. Dealerships just replace it and charge you some big money though.
I don't have any experience regarding P1633 and I can't give you any particular ideas.
These are just the basics of the troubleshooting. The 1st step is to check the regulated low voltage DC lines. Are the voltages all correct and well regulated? Aren't there any voltage ripples? The low voltage lines use electrolytic capacitors of low voltages and you can assume which lines are so.
Next comes the power up initial reset signals and power down reset signals. Are these generated properly? So far is the basic troubleshooting.
In your case, you also need to check the signal from the throttle position sensor. I worry that it might have some continuity or glitch problem. Since there is no manual and you have to be patient to do the reverse engineering deeply if you don't like to visit any dealership.
I don't have any experience regarding P1633 and I can't give you any particular ideas.
These are just the basics of the troubleshooting. The 1st step is to check the regulated low voltage DC lines. Are the voltages all correct and well regulated? Aren't there any voltage ripples? The low voltage lines use electrolytic capacitors of low voltages and you can assume which lines are so.
Next comes the power up initial reset signals and power down reset signals. Are these generated properly? So far is the basic troubleshooting.
In your case, you also need to check the signal from the throttle position sensor. I worry that it might have some continuity or glitch problem. Since there is no manual and you have to be patient to do the reverse engineering deeply if you don't like to visit any dealership.
The following users liked this post:
BNastee (09-18-24)
#4
Yamae, could a person build a test bench of sort for the ecu? And could you just power it up and not need all the other connections made to it, to check what you have just described? It just could be a lot of trouble to check such things while its in the car especially if there is no garage or shop to put it in and its raining outside.
#5
Moderator
Yamae, could a person build a test bench of sort for the ecu? And could you just power it up and not need all the other connections made to it, to check what you have just described? It just could be a lot of trouble to check such things while its in the car especially if there is no garage or shop to put it in and its raining outside.
#6
Since its a 12v system in the car isn't that all a person needs to power the ecu? Do you ever use a logic analyzer? I suppose a person could use some variable resistors to simulate some of the sensors.
Trending Topics
#8
#9
Driver School Candidate
Thread Starter
Thanks for the replies.
I replaced the battery with a new one late last year, but i havent checked the alternator yet. I'll give that a shot along with the Throttle position sensor and throttle control motor. Could a loose or bad accelerator cable do this as well?
Thanks again
I replaced the battery with a new one late last year, but i havent checked the alternator yet. I'll give that a shot along with the Throttle position sensor and throttle control motor. Could a loose or bad accelerator cable do this as well?
Thanks again
The following users liked this post:
BNastee (09-18-24)
#11
Moderator
Thanks for the replies.
I replaced the battery with a new one late last year, but i havent checked the alternator yet. I'll give that a shot along with the Throttle position sensor and throttle control motor. Could a loose or bad accelerator cable do this as well?
Thanks again
I replaced the battery with a new one late last year, but i havent checked the alternator yet. I'll give that a shot along with the Throttle position sensor and throttle control motor. Could a loose or bad accelerator cable do this as well?
Thanks again
Other than that, check the low voltage power supply circuits in the ECU. Attached photo below is a part of those. See the metal film resistor at the bottom end and compare the color of it with the one 100Ω at nearly the top. Those 2 resistors were originally colored same. The one 2.7Ω at the bottom is obviously semi burnt and the resistance is bigger than 2.7Ω and this causes malfunctions of the ECU when the battery voltage is lower caused by too much loads or poorly working alternator. I sometimes find this problem among Gen2.5 Celsiors.
The following users liked this post:
BNastee (09-18-24)
#12
I don't think that a loose or bad accelerator cable causes your problem. I'd rather think that the throttle position sensor or the related circuit causes it.
Other than that, check the low voltage power supply circuits in the ECU. Attached photo below is a part of those. See the metal film resistor at the bottom end and compare the color of it with the one 100Ω at nearly the top. Those 2 resistors were originally colored same. The one 2.7Ω at the bottom is obviously semi burnt and the resistance is bigger than 2.7Ω and this causes malfunctions of the ECU when the battery voltage is lower caused by too much loads or poorly working alternator. I sometimes find this problem among Gen2.5 Celsiors.
Other than that, check the low voltage power supply circuits in the ECU. Attached photo below is a part of those. See the metal film resistor at the bottom end and compare the color of it with the one 100Ω at nearly the top. Those 2 resistors were originally colored same. The one 2.7Ω at the bottom is obviously semi burnt and the resistance is bigger than 2.7Ω and this causes malfunctions of the ECU when the battery voltage is lower caused by too much loads or poorly working alternator. I sometimes find this problem among Gen2.5 Celsiors.
Getting the ecu repaired for my 98 LS400, replacing capacitors etc. My guy noticed that this specific 2.7 ohm resistor (R862) is partially fried on my board, slight discoloration and reads 3.1 ohms. Do you know the wattage for this resistor? Or can you point towards an adequate replacement resistor?
Best regards
The following users liked this post:
BNastee (09-18-24)
#13
Moderator
Hi yamae,
Getting the ecu repaired for my 98 LS400, replacing capacitors etc. My guy noticed that this specific 2.7 ohm resistor (R862) is partially fried on my board, slight discoloration and reads 3.1 ohms. Do you know the wattage for this resistor? Or can you point towards an adequate replacement resistor?
Best regards
Getting the ecu repaired for my 98 LS400, replacing capacitors etc. My guy noticed that this specific 2.7 ohm resistor (R862) is partially fried on my board, slight discoloration and reads 3.1 ohms. Do you know the wattage for this resistor? Or can you point towards an adequate replacement resistor?
Best regards
Last edited by Yamae; 09-14-24 at 10:13 PM.
The following users liked this post:
BNastee (09-18-24)
Thread
Thread Starter
Forum
Replies
Last Post
gp2m
LS - 1st and 2nd Gen (1990-2000)
69
05-08-21 08:48 PM
Aristsojzs
LS - 1st and 2nd Gen (1990-2000)
5
12-04-16 10:34 AM
PjLex
LS - 1st and 2nd Gen (1990-2000)
9
02-15-13 01:12 PM