Fixing A P0500 Check Engine Light By Re-Soldering The Instrument Cluster

Summary

For anyone that's interested, this post describes my experience in resolving a P0500 check engine light code on a 2nd Gen Tacoma instrument cluster.


Background Symptoms

I have a 2005 2nd Gen Tacoma V6 Auto 4WD with 315,000mi and it's been showing intermittent check engine light with code P0500 for the last year. P0500 is a failure in the VSS (vehicle speed sensor) signal at the ECM (computer). Driving with a OBDII scan tool hooked up, showing VSS live data, shows intermittent no speed signal. However speedometer works normally when the VSS signal drops out.


How It Works

On the 2nd Gen Tacoma V6 Auto configuration, the vehicle speed sensor originates at the four ABS wheel sensors, is processed through the ABS computer, then sent to the instrument cluster, displayed as speed on the speedometer, and reprocessed / conditioned and sent to the ECM (as well as the cruise control, 4WD module, and inverter if installed).
Wheels -> ABS System -> Instrument Cluster -> ECM


Diagnosis

Since the speedometer displayed normal speeds when the VSS signal to the ECM dropped out, this means that the failure is almost certainly in the instrument cluster, and definitely not in any upstream components. In other words since speedometer worked, that means ABS and the four wheel sensors are OK. The instrument cluster itself needs service.


Potential Fixes

This is not a rare issue on 2nd gen Tacomas, and can lead to much frustration chasing diagnosis. There are a number of shops online that specialize in Tacoma instrument cluster rework (google Tacoma P0500 fix to find them). There is also a bypass workaround described in another TacomaWorld post that shows how to feed the input VSS signal from C9-6 directly to the output C9-19 (see references below). I wanted the cluster fixed and not bypassed, but unfortunately, in six months of searching, I was unable to find out *what* component fails or how these clusters are being reworked in repair shops. I suspected a cold solder joint, since the error code seemed to most frequently appear shortly after starting the truck on cold mornings, as the cab was warming up. Temperature-sensitive failures are often due to poor / cold solder joints.


Evaluating the Cluster

I figured it was worth a shot to try to find the cold solder joint myself. There are videos online that show how to remove the Tacoma instrument cluster -- easy, takes about 10 minutes with minimal tools. There is also a video online that shows how to disassemble the 2nd Gen Tacoma instrument cluster (with the purpose of replacing the LEDs). I figured I could learn SMD soldering and rework in about the time (and with similar expense) as it would take to send the cluster off to a repair shop, and if I couldn't fix it, no big deal at least I learned something.

The Factory Service Manual and some online posts indicate that the VSS signal from the ABS system enters the instrument cluster on pin 6 of connector C9. The processed VSS signal leaves the instrument cluster from pin 19 of connector C9.

VSS Signal Path: ABS System -> Cluster Pin C9-6 -> Signal Conditioning Circuit in Cluster -> Cluster Pin C9-19 -> Engine Computer

Disassembly and inspection of the instrument cluster showed no obvious failed solder joints. Using a microscope, I was able to trace the circuit path from C9-6 to an area just to the left of the speedometer motor, and then trace the circuit path from this area back to the output on connector C9-19. Drawing out the schematic of the components in this area revealed two transistors that are likely doing the signal reconditioning, as well as a bunch of supporting resistors, capacitors, and diodes. See photos below. Likely if there was a cold solder joint, it was going to be on one of these components.


Learning SMD Soldering

It took a few evenings to learn SMD (surface-mount device) soldering -- an essential skill for reworking the cluster as the components are very tiny and I didn't want to make things any worse. Using 0.3mm 63/37 solder, flux paste, a temp controlled soldering iron at 350C, and a microscope, I used a SMD practice kit to get comfortable with installing, removing, and reworking SMD devices. 99.9% isopropyl alcohol was used for cleaning. There are plenty of youtube videos that show SMD soldering techniques.


The Fix

After I felt comfortable reworking SMD devices, I re-soldered all of the connections in the areas involved in the VSS signal processing, then cleaned with isopropyl alcohol. See the photos further down for the area of the board and the parts that I specifically reworked, marked in yellow and red. Reassembly of the instrument cluster and reinstallation is fairly straightforward. The issue now seems to be fixed - rather than setting the check engine light every second trip or so, the Tacoma has now been driven 400 miles on > 50 restarts with no signal dropouts.


Conclusion

For this particular set of symptoms - an intermittent P0500 error code with a working speedometer - there's a chance that the issue is due to a cold solder connection on the instrument cluster. Reworking the SMD solder connections on the part of the cluster involved in speed signal processing can be a quick fix to the issue.

Maybe this info can help someone else -- I know TacomaWorld has helped me in the past as a source of really great and hard to find information.



Parts and Supplies:

SMD Soldering Practice Kit

$9 Gikfun DIY SMD SMT Welding Practice Soldering Skill Training Board Ek7028

https://www.amazon.com/dp/B00VWB8F8K?ref=ppx_yo2ov_dt_b_fed_asin_title

MG Chemicals 8341 Flux Paste

$17 MG Chemicals - 8341-10ML 8341 No Clean Flux Paste, 10 milliliters Pneumatic Dispenser (Complete with Plunger & Dispensing Tip)

https://www.amazon.com/dp/B00425FUW2?ref=ppx_yo2ov_dt_b_fed_asin_title

MG Chemicals 824 Isopropyl Alcohol 99.9%

$19 MG Chemicals - 824-1L 99.9% Isopropyl Alcohol Electronics Cleaner, 945 mL (1 Quart) Liquid Bottle, Clear, 32 Fl Oz (Pack of 1)

https://www.amazon.com/dp/B005DNQX3C?th=1

0.3mm 63/37 Rosin Core Solder

$9 63/37 Rosin Core Tin Lead Solder Wire For Electrical Soldering(0.3mm/50g)

https://www.amazon.com/dp/B08M5XDKFG?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

Temp Control Soldering Iron Kit

$70 FNIRSI Soldering Iron Kit, DC/PD(96W/65W) Mini Digital Soldering Iron, 180-780℉ Fast Heating, 6 Soldering Tips, Digital OLED Screen Display, Auto Sleep (With Power Adapter)

https://www.amazon.com/dp/B0C1G9MNNT?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

7" Digital Microscope

$70 7'' Digital Microscope 1200X,Dcorn 12MP 1080P Photo/Video Microscope for Adults Soldering Coins,Metal Stand,Wired Remote,10 LED Fill Lights,PC View,Windows/Mac Compatible

https://www.amazon.com/Microscope-Dcorn-Magnification-Soldering-Compatible/dp/B08K7FGY9Q

Digital Microscope Arm Stand
https://www.amazon.com/dp/B0C1G9MNNT?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

OBDII Scan Tool for Simple VSS Display

$60 ANCEL BD310 OBD2 Scanner Diagnostic Tool - 3 in 1 OBD2 Scanner Bluetooth - App Based OBDII Scan Tool for Android & iPhone - Check Engine Light Code Reader - Wired, Bluetooth, and Heads-up Display

https://www.amazon.com/dp/B07J51W9NS



Helpful References:

2nd Gen Tacoma Instrument Cluster Removal
https://www.youtube.com/watch?app=desktop&v=Tr6tG8VFVlM

2nd Gen Tacoma Instrument Cluster Disassembly
Video for cluster disassembly: https://www.youtube.com/watch?v=VyEDHtdHx2M&t=334s

Clearing P0500 Fault With C9-6 to C9-19 Bypass
https://www.tacomaworld.com/threads/clear-a-single-code-to-pass-inspection.802680/


Photos:

(instrument cluster)
(microscope workstation)
(my crude schematic)
(backside of the cluster showing SMD devices)
(one part of the cluster that needed rework)
(the other part that needed rework)

 

Excellent information, I'll add a link to this in my writeup on the P0500 that can be found here.
https://www.tacomaworld.com/threads/2nd-gen-information-diagnostics.784008/#post-28042157

My suspicion was that it was a solder joint issue but this is the first one I've seen confirmed and repaired, we were just recommending bypassing them since the signal in and signal out is the same by cutting the wire at C9 Pin 19 and connecting it to C9 Pin 6.

Clear a single code to pass inspection | Tacoma World

 

Thanks DM93! Yeah thanks so much for that writeup on the C9-6 to C9-19 bypass. Knowing that the bypass was possible gave me the confidence to try the rework, since if it didn't help, I'd just end up using your bypass instead.

The oscilloscope graph above was a big help too. I also had a 'scope hooked up to the C9-19 speed output from the cluster (referenced to ground), and drove around with it like that for a few weeks. I could totally see when the signal would fail (usually on a cold morning) as the signal would go "high" and stay there. A few minutes later it was back to the normal square wave, presumably as the solder joint came back together. Of course by then the CEL had tripped with the P0500 again.

One curious thing -- I was seeing a +5V square wave on the cluster output to the ECM, but looks like you were seeing a +12V square wave. Maybe there are some differences in models out there.


I appreciate you guys!

 

Welcome!!
Awesome and helpful first post!

 

It seems to depend on which modules are equipped, some modules output a 5v signal and some output a 12v signal, seems to be an average of whats on the SPD circuit. I stated in my post that voltage on the SPD circuit may vary.

 

Great post! Any tips for pulling and reinstalling the needles?