Service Eng Soon Light Cranks Shaft Sensor '99 Silverado

A Chevy dealer just replaced my computer in my 99 Silverado V8 1500 4X4. When I picked it up that evening, the Service Engine Soon (SES) light was on. I take it back the next morning and the Service Mngr scans and advised the Crank Shaft Position Sensor (CSPS) was bad. He said it was reflected in multiple data appearing on his screen (he pointed at two or three vertical locations) and the CSPS needed replacing.

I took the vehicle to friend who runs a garage and who has for years routinely worked on all my vehicles. He scanned the vehicle...his reading reflected that the computer had not completed the "re-learn" process; however, he could not turn off the SES light.

I never saw what the Service Manager was reading on his scanner, but my friend was certainly was accurate in his reading based on the code(s). By the way, my truck has run fine for probably 20 miles of driving since the SES light was first noticed.

Any ideas?

Welcome to AF, first lets get you in the proper forum below in the truck/Siverado area. Second exactly what is the code?

Sorry, I don't have the code(s) from either source.

Sorry, I don't have the code(s) from either source.


with the DTC we can help you get going in the correct direction to resolve this issue of the check engine light...


how did you get to this point exactly from the begining...prior to the dealership making part replacements, with no corrective results...

A Chevy dealer just replaced my computer in my 99 Silverado V8 1500 4X4. When I picked it up that evening, the Service Engine Soon (SES) light was on. I take it back the next morning and the Service Mngr scans and advised the Crank Shaft Position Sensor (CSPS) was bad. He said it was reflected in multiple data appearing on his screen (he pointed at two or three vertical locations) and the CSPS needed replacing.

I took the vehicle to friend who runs a garage and who has for years routinely worked on all my vehicles. He scanned the vehicle...his reading reflected that the computer had not completed the "re-learn" process; however, he could not turn off the SES light.

I never saw what the Service Manager was reading on his scanner, but my friend was certainly was accurate in his reading based on the code(s). By the way, my truck has run fine for probably 20 miles of driving since the SES light was first noticed.

Any ideas?

I think your friend is right on. Whenever a VCM is replaced a procedure called "CKP System Variation Learn" is needed. It requires a high end engine capable scan tool to access this mode in the VCM. The dealer should have done this, but ??

PS. We really need the codes to verify this.

The vehicle was running normally, but cut off as if there were a fuel pump or fuel line issue. Towed in to my mechanic, and as best as I can describe...the fuel pump/fuel line was ok, but could not get power to run the fuel pump. Fuse issues were ruled out and my mechanic "hot wired" to the fuel pump, bypassing the fuse/relay, allowing me to drive the vehicle to the dealership for Chevy analysis. The drive in involved rough gear changes apparently due to the "hot wiring" or compurter problem, I'm not really sure.

The dealership determined the computer was bad, replaced it, and informed me the vehicle was ready. I pick it up in the evening after making payment earlier in the day, discovering the Ser Eng Soon light on as I crank the vehicle. I report the problem first thing the next morning.

Maybe I can call and obtain the code(s) observed.

the problem you described cutting out like fuel pump issue ,,,,,
could be loss of suffecient fuel pressure...

your mechanic must measure the fuel pressure as well as any DTC stored in the computer....

this vehicle requires 53-62 psi of fuel pressure...if the vehicle has 170,ooomi it is common that the fuel pumps go..at this mileage...

running the vehicle with little fuel will also kill these pumps fast ...

if it is a pump use the delphi pump...other pumps like airtex are defective...replace the filter and relay also ...


forgot to ask what engine,,,??? 5.3L or the old 5.7L....as the 5.3L pressures are what I gave you..

My mechanic considered putting a new Crank Shaft Sensor on to determine if the Check Eng Light goes off. He and the other guys in the shop pointed it out and I can complete this and I intend to do so. If the light's still on, I'll put the old sensor back on and go from there.

I didn't ask my mechanic, but if the new sensor is put on and this was the problem, would that cause the Check Eng Light to go off? I guess that's the objective, to confirm if it's in fact the sensor. Or if it's still on, then perhaps a System Variation Learn may not have been done.

They checked the pressure while ruling out a bad fuel pump and too, after the dealership later replaced the computer, the vehicle did run normally. So, apparently the fuel pump was never the problem

the problem you described cutting out like fuel pump issue ,,,,,
could be loss of suffecient fuel pressure...

your mechanic must measure the fuel pressure as well as any DTC stored in the computer....

this vehicle requires 53-62 psi of fuel pressure...if the vehicle has 170,ooomi it is common that the fuel pumps go..at this mileage...

running the vehicle with little fuel will also kill these pumps fast ...

if it is a pump use the delphi pump...other pumps like airtex are defective...replace the filter and relay also ...


forgot to ask what engine,,,??? 5.3L or the old 5.7L....as the 5.3L pressures are what I gave you..
It's a 5.3L and as indicated in the other reply, the pressures were in the correct range.

It's a 5.3L and as indicated in the other reply, the pressures were in the correct range.
...for what it's worth, my vehicle has 92,000 miles.

...for what it's worth, my vehicle has 92,000 miles.

with the mileage of this vehicle low and the computer was replaced ,,,I would very carefully clean all the ground points in the engine bay area as well as the ground point on the frame rail under the driver side rear of front wheel....in most cases the computer gets damaged from poor grounds....as well as jump starting ,,,and placing the charging cables reversed...

on a 5.3L engine the crank position sensor is under the starter motor....it has had problems with a few vehicles...

with the removal of the starter motor the sensor replacement is not difficult...

CKP=crank pos sensor..

I was back at my mechanic this morning to have them replace the Crank Shaft Sensor (CSS) since I could not locate it. Also, if this wasn't the problem, they could return the CSS and get reimbursed whereas I couldn't.

Since they're friends of mine, they got me in to do the install. Since not in the typical location they were familiar with, my mechanic called the dealership. Found that it was positioned back behind motor or somewhere impossible to reach and learned determined the dealership would be better suited to do the install and that the dealership would need to reprogram once installed.

My mechanic then explained what vehicle he was working on and that I had been there eariler reference the Check Engine Light. The contact was asked if there was some chance the dealership had not done the Verification Learn after installing the new computer. The contact thought that would have been done, but it was possible it wasn't. The dealership contact tells my mechanic to have me come back and they would do another scan.

I return to the dealership and a mechanic, different from those dealt with initially, advised that the scan reflected that the CSS had not been re-programed, but he had done so and cleared the Check Engine Light. I ask what his scan actually read and it was the same scan as my mechanic had obtained yesterday, now known as Code: P1636, specifically relating to the verification learn issue. He also volunteered that the mechanic who did the computer install was a large truck mechanic and he unknowingly failed to do the programing of the CSS.

I later called the Service Manager who did the initial scan yesterday afternoon...He said he couldn't recall the code he received, but his scan indicated the CSS "wasn't communicating" or that the CSS "wouldn't do anything." He said it just read, "Crank Shaft Positioning Sensor." He specifically said he did not get the CSS re-learn code. Based on his scan he thought the CSS was bad and needed replacing. The original mechanic, who was present when the Service Mngr did the scan, had agreed with the "bad" CSS as I was standing there. The Serv Mngr said the computer install mechanic and himself included, did not know that the CSS had to be re-programed separately from the Verification Learn which was done. He said the vehicle wouldn't have run if they hadn't done the Verification Learn after the computer was installed. I asked if there was anything else that needed to be programed separately and he said no, if that were the case, the light would still be on.

In the end, while I lost time from work and research to include this forum, I saved myself $168.00. Main thing is, my vehicle is back on the road where it belongs. The time on the forum and internet searches wasn't a waste by any means...I now know what a Crank Shaft Positioning Sensor is along with some computer issues.

Personally, but I'm wondering if the initial scan was a P1636, same as my mechanics and the dealership's last scan and it was obvious that the programming was all that was needed. The intent was for me to give them back the vehicle, they either do or don't replace the CSS (I'm guessing probably they don't cause I would never know otherwise), but charge me for it, then do the CSS re-learn, turn off the Service Eng Light and make an extra $168.00. Somebody let me know if I'm off base?

Thanks for the responses received and efforts to assist. You were helpful.

DTC P1636 PCM Stack Overrun I don't know how these people get to thinking the CKP has anything to do with this dtc???

also CSS this is also something that is not what I would expect as an automotive term..