Scion P1603
up on piston head. Follow the Repair Procedure in this Service Bulletin
Quick answer
For a 2013 Scion iQ in the US, DTC P1603 is covered by NHTSA-posted manufacturer communication S-SB-0008-16. The bulletin states that P1603 may occur with rough idle and/or a momentary idle-speed drop, and that these conditions may be caused by excessive carbon build-up on the piston head. Follow the bulletin’s repair procedure through a qualified service facility.
This page separates verified manufacturer/regulator evidence from supporting material. Unsupported causes, repairs or safety conclusions are not guessed.
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1. What does P1603 mean?
For a 2013 Scion iQ in the US, DTC P1603 is covered by NHTSA-posted manufacturer communication S-SB-0008-16. The bulletin states that P1603 may occur with rough idle and/or a momentary idle-speed drop, and that these conditions may be caused by excessive carbon build-up on the piston head. Follow the bulletin’s repair procedure through a qualified service facility.
2. Technical explanation
Verified evidence links P1603 on the applicable vehicle to an official Scion/Toyota service bulletin, S-SB-0008-16. The bulletin says the MIL may illuminate with P1603, P1604, and/or P1605 and that the listed idle concerns may be caused by excessive carbon build-up on the piston head. The supplied evidence does not provide the complete repair procedure or diagnostic thresholds.
3. What system is affected?
Not yet established by verified evidence.
4. How serious is this code?
Unknown. The supplied evidence confirms an MIL/idle-related condition but does not assign a severity level.
5. Symptoms you may notice
- Rough idle condition.
- Idle speed momentarily drops at idle.
- MIL may be ON with P1603, P1604, and/or P1605.
6. Possible causes
- The bulletin states that the listed conditions may be caused by excessive carbon build-up on the piston head.
7. Can I still drive the vehicle?
Not yet established by verified evidence.
8. Can I charge the vehicle?
Not applicable based on the supplied evidence; this is a conventional-engine diagnostic bulletin. Drive/charge status is not established by verified evidence.
9. What you can safely do
- Arrange diagnosis by a qualified Scion/Toyota service facility.
- Provide the technician with DTC P1603 and reference NHTSA manufacturer communication 10132874 / S-SB-0008-16.
- Do not attempt piston-head or engine repair based solely on this summary.
10. Step-by-step troubleshooting
- Confirm whether the MIL is illuminated and whether P1603 is stored.
- Check whether rough idle or a momentary idle-speed drop is present.
- Have a qualified technician follow the Repair Procedure in S-SB-0008-16. Further diagnostic steps are not established by the supplied verified evidence.
11. When to contact service
Contact a qualified Scion/Toyota service facility for diagnosis and repair under S-SB-0008-16.
12. What the service center may check
- Retrieve and confirm DTC P1603.
- Assess for the bulletin-listed rough-idle condition and/or momentary idle-speed drop.
- Follow the Repair Procedure in S-SB-0008-16.
13. Possible repair or resolution
- The verified bulletin directs technicians to follow its Repair Procedure. The specific repair steps and final resolution are not included in the supplied evidence.
14. Affected vehicles
- Scion iQ · 2013 · US
15. Related TSBs / service bulletins
- NHTSA Manufacturer Communication 10132874: S-SB-0008-16, published October 20, 2016. It applies in the supplied data to the 2013 Scion iQ, US. The bulletin addresses rough idle, a momentary idle-speed drop, and MIL illumination with P1603, P1604, and/or P1605; it states these may be caused by excessive carbon build-up on the piston head.
16. Recall information
- Not yet established by verified evidence.
17. Official manufacturer information
Official source: NHTSA Manufacturer Communication 10132874, S-SB-0008-16: https://static.nhtsa.gov/odi/ffdd/tsbs/TSBS_RECEIVED_2015-2019.zip#nhtsa_id=10132874
19. Frequently asked questions
What does P1603 mean for a 2013 Scion iQ?
For the supplied 2013 US Scion iQ applicability, P1603 is addressed by S-SB-0008-16 in connection with rough idle, a momentary idle-speed drop, and possible excessive carbon build-up on the piston head.
Can P1603 occur with other codes?
Yes. The bulletin states that the MIL may be ON with one or more of P1603, P1604, and/or P1605.
Is excessive carbon build-up confirmed whenever P1603 is present?
No. The bulletin says the listed conditions may be caused by excessive carbon build-up on the piston head; it does not establish that this is confirmed for every P1603 occurrence.
Is this a recall?
Not yet established by verified evidence. The supplied source is an official service bulletin communication, not evidence of a recall.