Speed sensor replacment

[Andrew Gaskins]

Hey fellas, another issue with my 88 I didn't see on the forum, maybe I just suck at looking for stuff. I took the truck to midas for an oil change yesterday (dont laugh, I've got a torn ACL and didnt want to be crawling around under my truck with my bad knee lmao), they told me the serpantine belt was chewing into my lower radiator hose and upon further inspection at home they were right. So this morning I drove up the road to the autozone to grab the parts and my brake light started flashing at me, after some research I've figured out it's a code 9, open circuit to speed sensor. Another part I've never had any experience working on, any advice on replacing it?

 

[PlayingWithTBI]

I'm confused, did you put in a different ECM than the OEM 1227747? Code 9 on an '88? Code 24 is for VSS (Vehicle Speed Sensor). Brake light flashing? Should be the CES (Check Engine Soon) light flashing after you short pins A & B in the OBD1 connector. Or am I totally washed up? LOL

 

[Andrew Gaskins]

I'm confused, did you put in a different ECM than the OEM 1227747? Code 9 on an '88? Code 24 is for VSS (Vehicle Speed Sensor). Brake light flashing? Should be the CES (Check Engine Soon) light flashing after you short pins A & B in the OBD1 connector. Or am I totally washed up? LOL

I'm confused to lmao, but everything I've read said if the brake light is flashing its normally an ABS issue. I've read break down after break down and other peoples problems. Similar to mine, when I went down the road and saw the light flashing I noticed my speedo wasnt working. After cutting it off and back on speedo worked but the flash wont go away. I read to short A and H, but it didnt give me any new pattern than what I had already seen. I'm bout to go short A and B and see what I'm getting.

Side note, i read with the parking brake light you read it at the start of the long flash and then the pulses and they all make up the code, the long flash is just the start of the code. I know that on the check engine light the long flash is typically the first digit and the pulses are the second.

 

[Andrew Gaskins]

I just shorted A and B. I got a code 12 from the check engine light. Got my speed sensor from autozone. I got underneath the truck earlier and the pin connected to it is caked in grease. Gunna replace the sensor, clean the plug and hope for the best. Definitely seems like a plug and play deal, I was just looking for any advice or things to know going in. I'll post an update here soon.

 

[PlayingWithTBI]

That's correct, the SES light will flash 1 - 5 times then a pause and flash 1 - 5 times again so, code 24 will be;
flash flash, pause, then flash flash flash flash. If it only flashes one time, pauses then flashes twice there's no code stored. Depending on how your bin is set (mine's set to 3), the code may go away after you turn off the key.

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Malf Flags in 7747 bin

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[Andrew Gaskins]

Replaced the sensor and all is well. Took it around the block after to make sure the speedo worked and it's all good. Disconnected the battery and the brake light finally stopped flashing me like I'm the lead singer of a boy band lmao. Tomorrows project is the lower radiator hose and serpantine belt, what fun lol.

 

[c1500deathtrap]

You sure laugh at your computer alot.

 

[Schurkey]

1. Flashing brake light is not the same as flashing SES light.

2. If the VSS sensor was bad, you'd ALSO have no functioning speedometer, no functioning cruise control, no functioning Torque Converter Clutch, no odometer, etc.

3. If the speedo, odometer, cruise, TCC, etc. is working, but the anti-lock isn't, and the anti-lock is telling you that the VSS is faulty, you've either got a faulty RWAL computer or you've got faulty wiring between the instrument cluster and the RWAL computer, or--maybe--a faulty instrument cluster.



I spent some time trying to diagnose my '88 K1500 for intermittent no speedo, no odo, no cruise, no TCC, and no RWAL. I had a faulty instrument cluster. The VSS and the VSS wiring was OK.

 

[88monteSS]

I'm confused, did you put in a different ECM than the OEM 1227747? Code 9 on an '88? Code 24 is for VSS (Vehicle Speed Sensor). Brake light flashing? Should be the CES (Check Engine Soon) light flashing after you short pins A & B in the OBD1 connector. Or am I totally washed up? LOL

The RWAL on the early trucks had separate codes from the ECM accessed by shorting A & H.

 

[evilunclegrimace]

I just shorted A and B. I got a code 12 from the check engine light. Got my speed sensor from autozone. I got underneath the truck earlier and the pin connected to it is caked in grease. Gunna replace the sensor, clean the plug and hope for the best. Definitely seems like a plug and play deal, I was just looking for any advice or things to know going in. I'll post an update here soon.

A code 12 is not an indication of a problem it just tells you that the ECM diagnostic system is working. The SES light will flash code 12 THREE times and then flash any other stored codes. If there are no other stored codes code 12 will repeat until you exit the diagnostic mode. If the SES light does not flash a code 12 it is an indication of a short to ground in circuit 419, or an open in circuit 451. It is also possible that the ECM has a problem or the PROM/mem-Cal is faulty.