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Juan Crespo
Juan Crespo, Tech Trainer
Category: Toyota
Satisfied Customers: 1526
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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I have an 98 toy Tacoma 2.7 and need to test to my o2

Customer Question

I have an 98 toy Tacoma 2.7 and need to test for voltage to my o2 sensors, specifically the forward/sensor 1. We took it to a dealer and they said I have a short.
JA: Sometimes things that you think will be really complicated end up being easy to fix with a Toyota. The Toyota Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so he can help you best.
Customer: Our catalytic converter was stolen some years ago but has since been replaced, however we keep getting P0130 and P0135 codes. We have replaced both sensors. Still get the codes a DAY OR TWO AFTER RESETTING THE check engine light. I have a schematic of the ECM and o2 sensors but need to check for a short in the harness.
JA: Are you hoping to fix this yourself?
Customer: Yes but I don't know which pins on the electrical connector to check for voltage.
JA: Great! What have you tried so far?
Customer: I have taken the glove box out and have check continuity to the sensors which seems to be good from the ECM to the sensors. Ground is good to sensors. The only wire I haven't checked (white w/ red stripe) goes from sensor to Junction block 3 under the dashboard.
JA: Is there anything else the Toyota Mechanic should be aware of about your Toyota?
Customer: The test the dealer preformed confirmed that there is voltage to one sensor but not to the other. ECM voltage is good, ohms of both sensors is good.
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Toyota Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: Toyota
Expert:  Juan Crespo replied 1 year ago.

Hi there. Thank you for using my services!

OK. First thing I need you to know is that I'm on your side and my only goal is to help you solve this issue. Having said that, and me not knowing your skill level, I need to establish a common language so we can communicate without confusing one another. For example, "a short" means a short-to-ground; "an open" means a broken or disconnected wire; "system voltage" means whatever voltage can be measured across the batery terminals at the time; "power" means current; "ground" means 0 volts. You OK with that so far?

Customer: replied 1 year ago.
I appreciate you help. I am a aircraft mechanic with 12 years experience and have been working on my vehicles since I was 16. On the automotive side I don't have the day to day experience that you have, but consider myself pretty handy.
Expert:  Juan Crespo replied 1 year ago.

I'm glad we're on the same page.

We'll be working with heated Oxygen sensors, which means there are two different circuits involved, heater and sensor signal. Now, let's start with the codes;

P0130 sets when the onboard computer (PCM) detects voltage from the Bank 1 Sensor 1 staying at a fixed voltage without switching from lo to hi as it normally should.

P0135 sets when the PCM detects more than 2 Amps from the Sensor 1 heater.

Since both codes pertain to the same sensor, I would start my diagnosis by conducting a thourough visual inspection of the wiring between the sensor and the PCM, including connector and terminal condition. If no issue can be seen, then I'd run continuity tests on the heater and signal circuit wires between the sensor and the PCM.

Go ahead and take a close look at those wires, then let me know if I still have to pull out the diagrams for you to do the continuity tests.

Customer: replied 1 year ago.
I am currently at work and will be home at 5pm GMT, I'm in Denver Colorado. I will look at this and get back to you. Thank you Juan.
Expert:  Juan Crespo replied 1 year ago.

Ahhh... the city that sits a mile high on the mountains. Brrr... Cold! Well, I'm sitting at sea level by the beach over 3000 miles away in balmy Dominican Republic!

Best Regards.


I'm on Atlantic time