99 Blazer 4x4 VSS issues with a twist
#11
CORRECTION IN POST #2: The EBCM monitors WSS data, and the PCM monitors VSS data.... don't ask, no clue on the reasoning there
Neither of the (front) WSS harnesses are shielded. The VSS harness is shielded, and the shield grounds to the "left rear of the engine". My guess is the rear of the left cylinder head On the schematic, it shows the two VSS wires running up to a connector at "the top rear of the automatic transmission". There are 4 wires in the connector, and they continue to the PCM. Another interesting thing about the shield, is that the schematic does NOT show the shield going the entire distance from the sensor, to the connector. They may have done that for the ease of presentation on the schematic, or to isolate the VSS signal from other sensitive circuits, (or vice versa) such as CKP and CMP sensors, again, who knows
Start with a good visual inspection of the harnesses from each sensor to its respective module.
Neither of the (front) WSS harnesses are shielded. The VSS harness is shielded, and the shield grounds to the "left rear of the engine". My guess is the rear of the left cylinder head On the schematic, it shows the two VSS wires running up to a connector at "the top rear of the automatic transmission". There are 4 wires in the connector, and they continue to the PCM. Another interesting thing about the shield, is that the schematic does NOT show the shield going the entire distance from the sensor, to the connector. They may have done that for the ease of presentation on the schematic, or to isolate the VSS signal from other sensitive circuits, (or vice versa) such as CKP and CMP sensors, again, who knows
Start with a good visual inspection of the harnesses from each sensor to its respective module.
Last edited by Captain Hook; 10-15-2015 at 03:07 PM.
#12
That harness is a nightmare. Thank you for that info. In order to thoroughly inspect that harness, I'd need to pull the cylinder heads, the transmission, or both. It's very possible that the connector behind the cylinder head has come loose, but it doesn't seem possible to reconnect it without removing the head. I did find out that the wires in question are indeed shielded twisted pair. So, I ordered some from an online supplier, and will be replacing that circuit. I'll update when that is done. Again, thank you for your help.
Last edited by mlprus; 10-16-2015 at 09:53 PM.
#13
I received my cable today. I installed it on the truck without any issues. I test drove the truck after installation, and I'm happy to report a successful repair. I'd like to sincerely thank you again for all of your help. I really do appreciate it. This is the cable I used : 2-Wire (Twisted Single-Pair) Tray Cable #16 AWG Shielded . It has the drain wire, to ground at one end, just like the original. It's in a PVC jacket, which is sunlight resistant, and oil resistant. 12 Ft of it cost me $14.01 with shipping. I'd post a link to it, but I don't know if that's allowed. Speedometer functions again, and transmission shifts as it should Again, thank you.
#14
Glad you got it taken care of.
In post #8:
WSS & VSS default to ~3MPH when the vehicle is not moving.
The absence of data from the LF WSS can be checked at the sensor connector using the VAC range on a DVOM. Rotating the wheel by hand should show ~350mVAC output from the sensor. With zero output, the ABS light should be coming on. If it's not coming on, I would suspect a software glitch in the scan tool. It is acknowledging the DTC in memory, but not seeing LF WSS data.
As for the absence of Trans ISS, (Input Shaft Speed) and OSS, (Output Shaft Speed) again, could be a glitch in the scan tool. The two signals are compared in the PCM for determining transmission slippage.
In post #8:
WSS & VSS default to ~3MPH when the vehicle is not moving.
The absence of data from the LF WSS can be checked at the sensor connector using the VAC range on a DVOM. Rotating the wheel by hand should show ~350mVAC output from the sensor. With zero output, the ABS light should be coming on. If it's not coming on, I would suspect a software glitch in the scan tool. It is acknowledging the DTC in memory, but not seeing LF WSS data.
As for the absence of Trans ISS, (Input Shaft Speed) and OSS, (Output Shaft Speed) again, could be a glitch in the scan tool. The two signals are compared in the PCM for determining transmission slippage.
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